Basic computer

Basic Computer course book
Free University of Bolzano Bozen – Dr. Paolo Coletti ‐ Edition 7.0 (8 October 2012)
Introduction
This book contains course’s lessons held at the Free University of Bolzano Bozen. It contains only the first
part of the courses, namely the lessons on:
 computer introduction,
 Microsoft Windows,
 computer networks,
 computer dangers and security.
It does not contain the parts on Microsoft Word, Microsoft Excel, financial functions, Microsoft Access,
computer algorithms, SPSS, Visual Basic for Applications, which are very well covered by the respective
courses’ suggested books.
This book is usually updated every year, please take a look at the edition date.
Disclaimers
This book is designed for very novice computer users. It often contains oversimplifications of reality and
every technical detail is purposely omitted. Expert users will find this book useless and, for certain aspects,
partially wrong.
This book supposes that the user is using Microsoft Windows 7 operating system in English language.
However, most of the book is perfectly readable with other Windows versions, while some menus and
instructions can be rather different if the language is not English (Windows language may be changed on
multi‐language installations: see page 6 for further information).
The novice user in this book is, for simplicity, always considered male. This is not meant to be gender
discrimination.
Table of Contents
Introduction .......................................................... 1
1. Computers .................................................... 2
1.1. Storage ......................................................... 2
1.2. Software ....................................................... 3
2. Microsoft Windows ...................................... 5
2.1. Versions and editions ................................... 5
2.2. Regional and language settings .................... 6
2.3. File system .................................................... 7
3. Computer networks ................................... 13
3.1. Technical aspects........................................ 13
3.2. Communication .......................................... 14
3.3. Internet connections ................................. 17
4. Computer security ..................................... 18
4.1. Encryption .................................................. 18
4.2. Passwords .................................................. 21
4.3. Viruses ....................................................... 23
4.4. Emails ......................................................... 24
4.5. Navigation .................................................. 26
4.6. Attacks from outside ................................. 27
4.7. Backup ....................................................... 28
Index .................................................................. 31

Dr. Paolo Co
Page 2 of 32
1. Com
This chapte
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Before star
terminology
Computers
called bit an
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Modern co
quantities:
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 Me
 Gig
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Paolo Coletti
Page 3 of 32
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Dr. Paolo Coletti Basic Computer course book
Page 4 of 32 Edition 7.0 (08/10/2012)
 private, software uniquely built, under payment, for a specific customer to fit his needs. Only the
costumer may use it. A typical example is the university’s students‐courses‐exams‐professors
database system.
The permission to be modified can seem a trivial question for the novice user, however for program
developers and computer experts being authorized to modify a software is a great advantage since it can
be improved, checked for errors and tailored to specific needs. The “open source versus proprietary
software” is a strong ethical and economical debate in the computer scientists’ community. Subdivision by
permission to modify is:
 open source software may be studied, used and especially modified by anyone. The software
developers at the same time legally authorize any modifications and they distribute the source of
the software to put other developers in a condition to easily modify it. Open source software is also
automatically freeware. The most typical example is Linux operating system.
 copyleft software is open source but carries the restriction that any modification must be
distributed as open source and copyleft, thus impeding that software becomes, after a
modification, proprietary. The most famous copy left contract license is the GNU Public License (see
http://www.gnu.org/licenses/gpl.html).
 proprietary software is distributed (costless as Adobe Acrobat Reader, or as a shareware as WinZip,
or most often sold as commercial software as Microsoft Office) with the explicit legal warning not
to modify it and technically locked to prevent other developers to see or modify its source.
1.2.2. Software naming
Software is usually identified by a name, for example “Linux” or “Microsoft Office”, sometimes by a
distribution/edition name “Linux Ubuntu”, “Microsoft Office Professional” and very often by a version
number, a sequence of numbers, points and letters (sometimes, as for Windows, commercial names) which
distinguishes the changes made by developers with time, such as “Linux Ubuntu 12.10” or “Microsoft Office
Professional 2010”. Obviously the version numbers of open source software changes rapidly, due to the
many developers working on them.
1.2.3. Data format licenses
Data need to be saved with a certain structure, called formats. For example, a plain text file may be simply
saved as a sequence of letters and symbols, which corresponds to the TXT format. More complex
structures, such as images, videos, but also formatted texts, need more elaborated formats to be stored.
These formats may be:
 closed proprietary, a format owned by a software company and kept as a trade secret. In this way
only programs build by that company can use those data files and no other company is able to
endanger its monopoly. A famous example is DOC format which, until 2007, was kept secret by
Microsoft, thus preventing competitors from building alternatives to Microsoft Word program.
 open proprietary,, a format publicly available but whose improvements and control are under the
ownership of a software company. A typical example is the new Word format DOCX.
 open, a publicly available format which follows official standards whose control is under ownership
of public organizations, such as American ANSI, German DIN or Italian UNI. Typical examples are
image’s format GIF or formatted text’s format PDF or web page’s format HTML.

Basic Computer course book Dr. Paolo Coletti
Edition 7.0 (08/10/2012) Page 5 of 32
2. Microsoft Windows
Microsoft Windows is currently the market leader operating system, it is the usual interface which appears
when the user turns a personal computer on.
2.1.Versions and editions
Microsoft released Windows XP in 2001 and for many years it has been the main Microsoft operative
system. In May 2012 it is still installed on approximately 30% of computers (source gs.statcounter.com).
Windows Vista was released in 2007 and it was not a market success.
Currently it is installed on less than 10% of computers.
Microsoft released Windows 7 in 2009, which is the currently default
Microsoft operative system. It is installed on approximately 50% of
computers. Its editions are:
 Starter and Home Basic, cheap versions with severe limitations, used
mostly on small notebooks;
 Home Premium, home user’s edition;
 Professional, personal business’ edition which includes more
network programs;
 Enterprise/Ultimate, Professional edition with more network utilities
available to companies/individual users. Enterprise edition is
currently (June 2012) installed at UNIBZ
2.1.1. Computer locking problem
Microsoft Windows sometimes becomes unstable: it can unpredictably, without any warning and when the
user does not expect it and typically when he is doing something very important and urgent, lock and
refuse to respond to user’s actions. When this happens, it is usually caused by the program that was used
and therefore the first thing to do is to try to close the current program. If this does not improve the
situation, the only other solution left is to turn off the computer. The list of operations to try until the
computer answers to user’s commands is:
1. if the mouse works, click the X button on the
program window or otherwise press ALT+F4;
2. press CTRL+SHIFT+ESC; select the program from the
list and press End Program;
3. press CTRL+ALT+DEL and, from the bottom right icon,
choose Shut Down;
4. press the computer on/off button;
5. unplug the electric power.
In any case all the current unsaved work will be lost; in the
last two cases the operating system can sometimes be
damaged but very often it will repair by itself the next time
the computer is turned on. Therefore it is always a very
good idea to save very often the current work, especially
when it is important, urgent, or difficult to redo.
Home Premium
Professional
Enterprise/Ultimate
Home Basic
Starter

Page 6 of 32 Edition 7.0 (08/10/2012)
2.2.Regional and language settings
With a multilanguage Windows installation, keyboard settings or menus’ languages may be changed
clicking on the Start icon”, choosing “Control panel”, then “Clock, Language and Region”, then “Change
Display Language”, and modifying the appropriate setting.
Another interesting
option, available on
every Windows
installation, is the
numbers’ and dates’
formats. When in
“Clock, Language and
Region”, choosing
“Region and
Language” and
clicking on “Formats”
then on “Additional
Settings” the user is
able to change the
format of numbers,
especially the
decimal separator,
the currency and the
date format,
especially the English
(month‐day) and
European (day‐
month) formats.
While the keyboard settings can be adjusted from this menu, it is easier to adjust it directly from the right
side of the application bar, simply clicking on keyboard icon and selecting the appropriate one.
2.2.1. Keyboards and languages
Before starting this section it is necessary to take a close look at your keyboard. Locate these keys since
they will be used in the rest of this manual and are very useful in many programs:
English keyboard German keyboard Italian Keyboard Main function
CTRL STRG CTRL
ALT ALT ALT
ALTGR ALTGR ALTGR Produce character on the key’s right left
F1 to F12 F1 to F12 F1 to F12
DEL ENTF CANC Delete next character
INS EINFG INS Toggle insert/overwrite mode
HOME or  POS1  Go to beginning
END ENDE FINE Go to end
PG and PG BILD and BILD PAG and PAG Go one page up or down

Basic Comp
Edition 7.0
BACKSP
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TAB
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Paolo Coletti
Page 7 of 32
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Dr. Paolo Co
Page 8 of 32
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Paolo Coletti
Page 9 of 32
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Dr. Paolo Co
Page 10 of 3
To compres
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user wants
indow.
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file. If the fi
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Page 12 of 32 Edition 7.0 (08/10/2012)
This mechanism, called roaming user profile, works fine only if the user is not using too much disk space
(which is usually 300 MB, but it is a good idea to stay below 150 MB). If the user is over quota, the system
sends a warning via email to the user and, if the user remains over quota, this mechanism does not work
anymore. Moreover, if the user still remains over quota, he will be forbidden from saving any file on the
computer he is currently using.
Therefore it is a good idea to always work on a USB pen drive (which is then copied on another personal
computer) and to periodically check the disk space looking at the proprieties of this directory. If a warning
email has been received or, even worse, roaming user profile does not work anymore, files need to be
deleted not from the current computer (since the mechanism is not working anymore) but directly going
through this directory.

Edition 7.0 (08/10/2012) Page 13 of 32
3. Computer networks
This part of the book is dedicated to computer networks from a user’s perspective. Nowadays a computer
is very likely to belong to some company’s network, or to be connected to the Internet via an Internet
provider, and is therefore exposed to all the typical network problems. Without entering into technical
details, this section will explore the situations in which a novice user can find himself in troubles and how
he can try to survive dialoguing with network administrators in their own strange technical language.
3.1.Technical aspects
A computer network is a set of devices which communicate and share resources. These devices are mostly
computers, and sometimes stand‐alone hard disks, telephones, printers and terminals (processorless
computers which must rely on other computers to work).
3.1.1. Server and client
A computer network interaction is based on the client server architecture. When considering a single
interaction, one computer is the server and the other one is the client. The server is the computer which is
offering its resource, usually programmed to wait until someone asks for its resource. The client is the
computer which uses the resource, which sends the request to a waiting server.
For example, when sending a document to the printer, the user’s computer is the client while the printer is
the server; when retrieving personal emails, the user’s computer is the client which connects to the
mailserver asking for available emails. When talking to a friend on an Internet chat, the interaction is
composed of two different interactions: the user’s computer as a client is connected to the chat room’s
computer acting as a server, and the friend’s computer does the same interaction.
The same computer may be the client for a service and the server for another service. For example, a
library computer may have a CD inside its reader shared to the network (server for the CD) and may be at
the same time used by a user to print his own documents (client for the printer).
3.1.2. Areas
Computer networks are commonly divided into three categories:
 Local Area Network (LAN or Intranet), usually the network of computers in the same building or
belonging to the same owner. Inside the LAN every computer is well identified and usually every
user is known. It is considered a trusted area.
 Wide Area Network (WAN or Internet), which is everything which connects LANs. Computers’ and
users’ identification is very hard and anonymity is possible. It is considered a dangerous area.
 Virtual Private Network (VPN) is a way to recognize a computer outside the LAN as a trusted
computer: the user is identified with a password and his computer, even though connected via
Internet, will be considered as part of the LAN, for as long as it remains connected. VPN is typically
required to identify portable computers connected via wireless connection.
3.1.3. Transfer speed
The network connecting components are the cables, which determine the speed of the LAN. Cables have a
speed measure in bps (bits per second) which indicates how many bits can flow through the cable in one
second.

Dr. Paolo Co
Page 14 of 3
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Edition 7.0 (08/10/2012) Page 15 of 32
3.2.3. Posta Elettronica Certificata PEC
When sending an email, the sender has no proof that it has been sent, for example to be used in a court of
justice, and no guarantee that the email has been dispatched. Some mail readers use a receipt system, but
the receiver is not obliged to send back the receipt.
In order to overcome these problems, many solutions have been proposed. The Italian Posta Elettronica
Certificata (PEC) system has become one of the most widespread solutions, thanks to law Decreto
Ministeriale 6 May 2009 which guarantees a free PEC email address to every citizen and thanks to law
82/2005 which determines that PEC receipts are legal proves.
When an email is sent from a PEC address to another PEC address, the sender receives two receipt: the first
one is a proof that the email has been sent with date and time, while the second one is a proof that the
email has been dispatched to the mailbox of the receiver. This does not represent a proof that the email
has been actually read, but from the moment the email is dispatched to the mailbox it is the receiver’s
responsibility to read it. Under this circumstances, it is perfectly equivalent to “raccomandata con ricevuta
di ritorno”. Emails can be send also from a PEC address to a non‐PEC address, and in this case the receiver
gets only the sent proof but not the dispatched proof, like the “raccomandata semplice”. When an email is
sent from a non‐PEC address to a PEC address, no receipt is produced and this is equivalent to a standard
letter.
Moreover, even though it is not officially required, PEC to PEC also guarantees that content be not altered
and that sender’s email address is the indicated one. However, it is important to note that PEC alone does
not guarantee that the sender is really the person who claims to be and that content remains unread until
it reaches destination. In order to overcome these last two problems, encryption and digital signature (see
section 4.1 on page 18) must be used.
3.2.4. Voice over IP programs
Voice over IP (VoIP) programs are able to use the computer connection as a substitute for standard
telephone. Equipped with either microphone and headphones or with a real telephone‐like device, the user
can send his voice through the Internet to remote computers or even to real remote telephones, thus
saving on telephone bills.
VoIP requires a subscription to a VoIP’s website, the most famous being Skype, who decides the telephone
fares. Typically calling other VoIP’s users is free all over the world, while calling fixed telephones depends
only on the destination country and is independent from the caller’s country, with a fare which is
comparable to the standard local telephone call (about 2 €cent/minute in June 2012). On the other hand,
calling mobile telephones is, for the moment, still very expensive (about 30 €cent/minute in June 2012); for
this reason, special VoIP telephones, which can be programmed to automatically decide between VoIP and
the standard telephone line according to the dialed number, are appearing on the market.
3.2.5. Search engines
A search engine is a special program running on a website which offers to the user the possibility of
searching other websites for specific web pages. The user needs to connect to the search engine website
and digit the keywords, or sometimes even a complete question, and the website returns the list of
relevant web pages.
Search engines use a crawler technique: they continuously go through the known web pages memorizing
their content and trying to discover other web pages through the contained links. In this way they are able
to memorize most of the WWW’s pages (more than 8 billion pages), even though some not linked websites
can remain unknown to search engines.

Dr. Paolo Co
Page 16 of 3
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doc or .pdf;
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c Computer
Edition 7.0 (0
ult:
often produc
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oids wrong r
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een;
e search of p
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course book
08/10/2012)

ces the right
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Edition 7.0 (08/10/2012) Page 17 of 32
3.3.Internet connections
There are many different ways to connect to the Internet, divided by the physical mean of connection: the
telephone cable, a dedicated cable or electromagnetic signals.
Broadband
ADSL (Asymmetric Digital
Subscriber Line)
telephone line
modem
500 Kbps in upload
8‐20 Mbps download
Speed depends on
subscription fee
and network traffic
Internet cable some Gbps
UMTS (Universal Mobile
Telecommunications System)
3G
UMTS cellular phone 7 Mbps
Speed depends
strongly on
environment
Wireless
Wi‐Fi
wireless card 30‐80 Mbps
Speed depends on
wireless generation
WiMax
antenna in line of sight
modem
40 Mbps
Speed depends
strongly on
distance
Many fast connections, especially ADSL, suffer from network congestion: too many users are connecting at
the same time and the Internet provider’s main cables are not able to support the users’ maximum speed
multiplied by the number of users, and therefore must reduce the practical connection speed. Therefore
the maximum speed is often only theoretical and some providers are offering a “minimum band
guaranteed”: a minimum speed under which the connection may never fall.
Unfortunately, even in technologically advanced countries, there are still many areas where nor ADSL
neither UMTS arrives, mostly due to the geographic conditions (mountains, islands or long desert distances)
and to the low inhabitants’ density. This phenomenon is called digital divide: there are people (e.g.
5,000,000 of Italian inhabitants) that even willingly to pay cannot get a broadband connection, and, on the
other hand, Internet services and especially the WWW is continuously going towards large size contents,
cutting these people off. In order to overcome this social problem, WiMax is spreading, a sort of very long
range Wireless which arrives up to 10 Km but works only if the transmitting and receiving antennas are in
line of sight and whose theoretical speed of 70 Mbps decreases with distances to about 40 Mbps.

Names Equipment Effective speed Notes
PSTN (Plain Standard
Telephone Network)
analogical
dial‐up
telephone line
modem
56 Kbps
Telephone is busy
during connection
ISDN (Integrated Service
Digital Network)
ISDN telephone line
modem
128 Kbps
Telephone is busy
during full speed
connection
GPRS (General Packet Radio
Service)
GSM cellular phone 100 Kbps

Dr. Paolo Co
Page 18 of 3
4. Com
Being conn
novice user
inside, with
the non‐exp
Moreover, t
techniques
access to pe
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Encryption
way that it
encrypting,
by all the c
thus the di
used.
The two fol
The sent m
intercepts a
is known on
The same p
using a secu
browser use
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32
mputer
ected to the
r’s belief tha
all its benef
pert user, to
the recent It
which must
ersonal data
ch user must
gerprint, han
ch user has
rmissions mu
ers must rece
ponsibilities,
rewall (see
sent, either
wall, are) or
tware used t
ery 6 months
data must be
sitive data r
e of loss, mu
cryption
is a text ma
may be corr
usually know
computers o
fficulty to b
llowing sche
essages are
a message, h
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es it to encry
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at he is the o
fits and dang
avoid being
talian law 19
be adopted
protected b
t be authent
nd shape, ey
its own pe
ust be revoke
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, duties and t
section 4.6.
installed ei
at the LAN e
to handle da
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ust be restore
n
sking techni
rectly read o
wn only to o
r people wh
e guessed, i
emas illustrat
encrypted a
he is unable t
n when some
ens whenev
on (see sect
ypt informat
rity
means giving
one who goe
gers. Knowin
lured into tr
96/2003 on p
by system a
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ticated by a
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training to b
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ither on eac
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ata must be
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ial care: the
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tes how B, C
and later dec
to decrypt it
ebody us
er a browser
tion 4.5 on p
ion which ca
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es outside, i
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raps or adop
privacy issue
administrato
ust take care
personal us
imited only
user does n
be able to us
dangers;
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ch computer
usually the f
updated at
4.6 on page
ey must be s
days.
d from milita
pecial passw
er or person,
tely may rea
in bits, wit
C and D can
crypted by A
t correctly sin
ses the publi
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page 26): the
an be read on
ccess to the
it is instead
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pting potentia
s contains in
ors but also b
e of these pro
sername and
to the dat
ot need them
se their auth
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firewall is);
least every
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stored and tr
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word called ke
and a privat
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send secret
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nce he does
ic key to dec
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nly by the ar
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the Internet
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te key for de
mation. The
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crypt, it does
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ls the brows
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Despite the
t world whic
adays neces
us behaviors
o B the mini
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particular:
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for his wo
and to be aw
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nformation t
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Edition 7.0
Another an
private and
automatica
instructions
password to
puter course
(08/10/2012
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Dr. Paolo Co
Page 20 of 3
4.1.1. Dig
A digital sig
the same ti
According t
The two fo
publish a p
key and
something
from A; on
private key.
and email’s
While encry
to create it
automatica
be sure tha
authority to
be sure that
having iden
when used
automatica
oletti
32
gital signa
gnature, or e
ime, the doc
o Italian law
ollowing sche
ublicly availa
d all the us
readable, it
the other h
. In this way,
content.
yption to rec
ts own coup
lly without t
at the publ
o distribute
t the user do
ntified him th
d together,
lly encryptin
document
false
document
ature
electronic sig
cument’s au
w 82/2005, di
emas illustra
able docume
ers can try
means that t
hand, if the
, digital signa
ceive secret m
ple of private
he user’s int
ic key is re
private and
oes not give
hrough a gov
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encr
gnature, is an
thor’s ident
gital signatu
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ent with its
to decrypt
the docume
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ature used in
messages or
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tervention), f
ally the aut
public keys.
the private p
vernmental i
to his priv
ts.
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ity and that
re is equival
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signature. It
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vate key. An
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decrypt
decrypt
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for documen
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ally a simple
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nts which gu
nt has not be
ature.
l signature.
ncrypt it with
result of d
vate key and
was not do
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the user or t
wsers, do th
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requires a
password is
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course book
08/10/2012)
uarantees, at
een altered.
A wants to
h his private
ecryption is
thus comes
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der’s identity

the program
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Basic Comp
Edition 7.0
Several Ital
as a smart
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private cer
private use
4.2.1 on pag
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The major d
many priva
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only to him
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(08/10/2012
ian public in
card and, us
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ocuments. T
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ge 22).
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drawback of
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manage to
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n when they
thief can do
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thief as wel
al money: t
ectly from th
book
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alternative
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find the righ
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with hand
Digital sign
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Some year
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the user. La
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d emails rece
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the thief can
he user’s web
re now using
rtification of
do not offe
to digitally
with prices
devices suc
keys is that
e and then t
ht private key
s has a tim
ypt again all
tant to dete
he certificatio
dwritten si
nature
s from certif
r tools
y (with prope
ome years
rs (can be ren
onds for all d
ols)
if temporal m
ed only by hi
makes an un
If somebody
w 196/2003
t from work
the thief can
ta: the thief
eived from o
r who did not
n find the u
b browser’s h
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user’s ident
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sign docum
currently a
ch as OTP de
t if a compu
to decrypt it
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the past doc
ermine the
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mark
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3 explicitly fo
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n read the us
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exact date
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ccess to dat
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ture of
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also by
section
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orrect public
ct encryption
ually some
of the signa
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rybody insta
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il other relia
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per’s and ink
everybody, a
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and persona
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data;
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ature have
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their passwo
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her people p
f this privacy
passwords,
Paolo Coletti
age 21 of 32
t a text with
within some
n. Therefore,
which it is
moreover a
no time
es are
nt
lements
word, known
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Dr. Paolo Co
Page 22 of 3
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trial: specia
passwords
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have some
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Obviously t
to avoid tha
oletti
32
ete and mod
se data with
ntent, add ille
al identity: f
rld exactly a
hdrawing fro
rt illegal act
mebody else
t is absolute
here are som
al automatic
each seco
ns of words
man and Eng
aw 196/200
features:
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oid words rel
e minimum 8
other good p
e as password
y common w
e different p
ister with a
bsite they r
sswords: one
mportant us
ware of passw
re your pas
m to be un
eal them ins
y if that com
mputer or th
blic places su
ne Time Pa
er a few seco
his system w
at the physic
dify data: th
hout the use
egal pictures
or the comp
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om exams;
tivities: anyb
identity, so
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ond, and t
and numbe
glish words
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sword often,
ated to your
8 characters.
procedures a
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passwords fo
password an
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words stored
ssword mas
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works in com
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body who w
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discover eas
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can be tried
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rself, such as
are:
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or different
nd users who
n untrustwo
ant use (bank
g to unknow
d in program
ked with as
but compute
re password
single user
aptop) or if a
ernet café.
evice
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very sm
every fe
OTP dev
seconds
mbination wit
eft of the OT
delete user’s
dge (bank nu
ef is now th
for example
wants to star
et into troub
sswords sec
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try one mill
y start try
mplete set of
in less than
at password
ery six month
s names, birt
rs, strange ch
es or words
purposes.
o use always
orthy ones.
k account), a
wn websites o
ms: mail read
sterisks. The
er experts ca
s in program
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access to tha
device is a
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vice and eac
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th another st
TP device res
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bles when th
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t Explorer an
is on a usern
ssword syst
hich display
m is perfectly
is accepted
assword is in
sword that t
mpletely secu
c Computer
Edition 7.0 (0
en worse he
addresses, de
e can act to
subscribing t
tivity will ob
discovered.
d addresses;
d capital lette
dictionary);
ebsite asks
e giving it aw
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ay use and a
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nd many oth
name basis,
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only if ente
tercepted o
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urity breach.
course book
08/10/2012)
e can modify
egree thesis
the outside
to websites,
bviously use
ers, avoiding
the user to
way to every
least three
last one for
nymore).
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Edition 7.0 (08/10/2012) Page 23 of 32
4.3.Viruses
From the Internet many unauthorized connection attempts arrive. Some of these are mistakenly authorized
and manage to reach the Intranet or at least to come in contact with programs which are behind the
firewall. If these connections carry malign intentions, usually their aim is to explore and use the Intranet
computers, to destroy Intranet data or to stop some Intranet services (which is a dangerous attack if these
services are managing stock trades or telephone calls). Defense against these kinds of attacks is in charge
system administrators.
While normal external attacks do not involve normal users, the virus is a special attack which arrives
directly on the user’s computer and must be prevented and stopped by him. The virus is a little program
which has this name because its life cycle is the same of a biological organism: survive and duplicate.
1. It arrives on the computer through email attachments, downloaded files, CDs and floppy disks or
directly from the Intranet. It is often hidden inside other good files or programs, which are called
infected.
2. As soon as the user mistakenly runs it (often trying to run the good program or to open the good
file), the virus orders the computer to run itself every time the computer is turned on, thus assuring
its survival.
3. It starts duplicating itself, infecting other files, CDs and floppy disks, and trying to send itself around
by email or on the Intranet.
4. Most viruses are programmed to do damage to the computer and to the user, altering or deleting
files, sending emails with user’s personal data, preventing firewalls and antiviruses from running, or
turning the computer off. No viruses are known to be able to damage hardware.
Many names are used for viruses’ types according to their different behaviors.
 trojan horse is a virus which looks like a good program and, when downloaded and run by the user,
it performs the user’s wanted task but at the same time does other actions;
 key logger is a virus which records keyboard’s activity and then sends the keystrokes to its creator,
mostly to get user’s passwords;
 back door is a virus which opens a port on the computer to let external users in;
 adware is a virus which displays advertisement;
 spyware is a virus which spies user’s activity to get passwords or to target the user with specific
advertisement;
 dialer is a virus which dials expensive numbers using the PSTN modem.
These types are not exclusive: for example a Trojan horse which is at the same time a spyware and an
adware.
An infected computer can be recognized by some symptoms. These are the most frequent ones:
 when the computer is turned on, unwanted programs start, advertisement appears, and the
desktop presents some new bars or features which were not present nor installed before;
 the computer starts very slowly and unknown programs give strange operating system errors;
 commercial or pornographic web pages appear on the web browser without the user’s consent;
 the analogical modem makes typical connection noises even when the computer is not connected
or the operating system asks the user to stop the current connection and start a new one to a
strange telephone number;
 the Task Manager window (see page 5) presents unknown programs.

Page 24 of 32 Edition 7.0 (08/10/2012)
Most of the time, a responsible user’s behavior it the best weapon against viruses: it protects him from
getting viruses, helps him removing them and prevents him from diffusing them. Responsible behavior
means:
 never open downloaded files and email attachments, especially when they come from a friend with
a text such as “please open it, urgent!”, since simulating to be a user’s friend is a typical virus
tactics. To open these files, save them on the desktop, check them with an antivirus and then open
them;
 do not insert in your computer CDs, DVDs and USB pendrives coming from other people or which
were inserted in other computers, unless you have an antivirus running or unless you scan them
immediately with an antivirus;
 avoid visiting strange websites, especially pornographic or hackers’ website, or websites which
open a lot of pop‐up windows;
 have an antivirus always running or at least run an updated antivirus on your whole hard disks
every week (while Italian law currently prescribes minimum every 6 months); keep your antivirus
always up to date: more than 50 new viruses appear every week;
 keep communication programs and Microsoft products up to date. Microsoft and most software
companies offer free updates and automatic updating tools.
To check the computer for viruses and to try to remove viruses from the computer, the user can run a
special program called antivirus. The antivirus basically has three possible different actions:
 it can scan all the storage devices (hard disks, the floppy disk inside the computer, the CD or DVD
inside the reader) for viruses. If a virus is found, it tries to remove it and to repair damaged files.
Some files can be unrecoverable. Complete devices scanning takes usually some hours;
 it can scan a single file or an entire directory for viruses. If there is an infected file, it tries to delete
the virus and repair it. Some files can be unrecoverable. Single file scanning takes some seconds;
 it can be always running. In this case, whenever a virus or a suspect file is run, the antivirus
prevents it from running and warns the user.
A lot of antivirus programs, free and commercial, exist. Their most important feature is obviously the
possibility to be constantly updated through the Internet.
4.4.Emails
4.4.1. Attachments
For viruses, email attachments are a first class way of traveling, since they are very often opened by users
without any precaution. Sometimes viruses hide inside files which were really sent by the sender, unaware
of having an infected computer. Other times a virus takes control of the mail reader program and sends
itself to the whole address book, counterfeiting the sender address (often using an address taken from the
address book) in order to avoid that the real infected computer be identified and to gain the thrust of the
receiver, and writing in the email text smart sentences pretending to be a regular friend of the receiver. The
arrival of this kind of email usually creates havoc, since the receiver is sure that the fake sender has a virus,
while the original infected computer is another one.
The basic rule is never open any attachment from the mail reader program. Save the attached files on the
desktop and run an antivirus program to check these files before opening them. Even when the email
comes from a friend: he cannot know that to have got a virus, or he can not be the real sender.

Basic Comp
Edition 7.0
4.4.2. Spa
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Dr. Paolo Co
Page 26 of 3
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www.athes
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Any compu
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age 27 of 32
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Page 28 of 32 Edition 7.0 (08/10/2012)
the point where the LAN connects to the Internet, or more often on every computer a special program
called firewall is running. The firewall examines all the incoming and outgoing traffic, using the following
analysis techniques:
 which internal program is originating/receiving the traffic,
 from/to which external address is the traffic originated/directed,
 what amount of traffic is passing from/to the same program to/from the same external address,
 which kind of data are passing.
Making an analysis of these data clearly slows down the connection but lets the firewall stop potential
unauthorized connection, putting them in a wait state until the user’s gives his approval or denial.
Windows Seven operating system comes with a firewall preinstalled, which lets the user customize which
kind of programs are allowed to make or receive connections and determine rules to approve or deny
automatically connections.
4.7.Backup
Backup is the process of copying important data to another location to prevent their loss. Sometimes
programs and even entire operating systems are copied, to be able to immediately continue working even
when a computer breaks. There are three very good reasons to do regular backups:
 against the user, who can accidentally delete some files or who can modify files and then change
his mind. Having a recent backup handy can often save hours of work;
 against the system, which can suddenly break due to hardware or software problems. Even hard
disks tend to be unreliable after some years of continuous activity. A recent backup saves the user
from redoing all the work of the previous months;
 against viruses and other users, which can delete and alter files: a backup can save a user coming
back from vacations.
Usually the operating system’s and the programs’ backup are done by system administrators: law 196/2003
explicitly requires an instantaneous backup for all sensitive data and that data are restored within 7 days in
case of loss. However, there are some files which should be taken in charge by the user himself:
 personally created data files, including all documents and images created by the user, and any
other file which is a result of the user’s personal work;
 the address book and the emails (mail readers usually offer a way to save them into files to be used
for backup), and for strong navigators also web browser’s configuration;
 some programs require a lot of configuration and store their configuration in configuration files,
which are usually in the program’s directory;
 all the stuff which is difficult to find again, such as documents from other people or downloaded
from forgotten websites.
The place where the files are copied determines the reliability of the backup. It should be a large, cheap
and fast storage device. It should also be handy, since the typical problem with backup is that the user does
not takes time to do it regularly and, when the backup is too old, it is worthless. For home or simple office
users, the Friday morning backup is a good timing solution. Good storage devices to be used are:
 a second hard disk, used only for backup, which is very fast and very large and always ready to be
used;

Basic Comp
Edition 7.0
 onl
(giv
offe
 fou
 USB
 big
4.7.1. RA
A very popu
of several i
functionalit
JBOD (Just
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RAID1 is th
two identic
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age 29 of 32
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Dr. Paolo Co
Page 30 of 3
RAID10 is a
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Basic computer

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