Computer viruses can infect computers through infected floppy disks or programs. There are two main types: file viruses, which infect executable files, and boot sector viruses, which infect the boot sector of disks. Viruses spread by replicating themselves and transferring to other disks or files. They can damage systems by corrupting or deleting files and programs. Users can prevent viruses by avoiding untrusted disks and files, updating antivirus software, and being wary of email attachments. Once infected, antivirus software must be used to detect and remove the virus.

1. Computer VIRUSComputer VIRUSbyby
PAYAL MISHRAPAYAL MISHRA
Regd.no-F1007703002Regd.no-F1007703002
ETCETC

2. What is a VIRUS ?What is a VIRUS ?
Virus is Vital Information & Resource under Seize. AVirus is Vital Information & Resource under Seize. A
computer virus is basically a program written for destructivecomputer virus is basically a program written for destructive
purpose. It is written in such a way that it can enter the com-purpose. It is written in such a way that it can enter the com-
putter without the knowledge of the machine or the user. Itputter without the knowledge of the machine or the user. It
enters the machine through an infected floppy or a program.enters the machine through an infected floppy or a program.
It has the capacity to make perfect copies of itself and causeIt has the capacity to make perfect copies of itself and cause
abnormal functioning of the machine.abnormal functioning of the machine.

3. Comparison between Biological &Comparison between Biological &
Computer Virus.Computer Virus.
 Both need a carrier to get into the system. An infected floppyBoth need a carrier to get into the system. An infected floppy
is the best example of vector for the virus to get into theis the best example of vector for the virus to get into the
system.system.
 Both are parasites, the computer virus is a parasite on theBoth are parasites, the computer virus is a parasite on the
computer system; it uses the computer resources like memorycomputer system; it uses the computer resources like memory
and the programs to replicate itself. It also spreads to otherand the programs to replicate itself. It also spreads to other
diskettes used on an infected machine.diskettes used on an infected machine.
 Both have the capacity to replicate themselves and henceBoth have the capacity to replicate themselves and hence
spread causing damage to their host.spread causing damage to their host.
 Both replicate to such an extent that they finally destroy theBoth replicate to such an extent that they finally destroy the
carrier used and the other programs/cells. The com- puter viruscarrier used and the other programs/cells. The com- puter virus
destroys the programs and data on the system.destroys the programs and data on the system.

4. Difference between Biological &Difference between Biological &
Computer Virus.Computer Virus.
The major difference between the two is that aThe major difference between the two is that a
biological virus causes physical harm to the organismbiological virus causes physical harm to the organism
attached, where as the computer virus does not causeattached, where as the computer virus does not cause
any physical damage to the system. But the harmany physical damage to the system. But the harm
caused by the computer virus to the data/programscaused by the computer virus to the data/programs
stored in it.stored in it.

5. Origin of VIRUSOrigin of VIRUS
Writing of self-replicating software ideaWriting of self-replicating software idea
was 1was 1stst
given by John von Nevnam.given by John von Nevnam.
Some programmers of AT&T worked onSome programmers of AT&T worked on
the project.the project.
Those programs strictly kept in AT&T only.Those programs strictly kept in AT&T only.
Illegal copying of self-replicating softwareIllegal copying of self-replicating software
was the development of Virus Software.was the development of Virus Software.

6. Types of VIRUSTypes of VIRUS
Basically 2 types of viruses are thereBasically 2 types of viruses are there
File virusFile virus
Boot Sector virusBoot Sector virus
FILE VIRUSFILE VIRUS
This virus infects only executable files e.g.This virus infects only executable files e.g.
.EXE,.COM files..EXE,.COM files.
BOOT SECTOR VIRUSBOOT SECTOR VIRUS
This virus resides boot sector of the disk.This virus resides boot sector of the disk.

7. Some examples of VIRUSSome examples of VIRUS
Name of VirusName of Virus Types of VirusTypes of Virus
AlabamaAlabama File VIRUSFile VIRUS
JerusalemJerusalem File VIRUS (Infect .COM & .Exe Files)File VIRUS (Infect .COM & .Exe Files)
Dark AvangerDark Avanger File VIRUS (Infect .COM & .Exe Files)File VIRUS (Infect .COM & .Exe Files)
DIR-IIDIR-II File VIRUS (Infect .COM & .Exe Files)File VIRUS (Infect .COM & .Exe Files)
CascadeCascade File VIRUS (Infect .COM Files)File VIRUS (Infect .COM Files)
BrainBrain Boot-Sector VIRUSBoot-Sector VIRUS
StonedStoned Boot-Sector VIRUSBoot-Sector VIRUS
Disk KillerDisk Killer Boot-Sector VIRUSBoot-Sector VIRUS
Bouncing BallBouncing Ball Boot-Sector VIRUSBoot-Sector VIRUS
Birthday JoshiBirthday Joshi Partition table VIRUSPartition table VIRUS

8. Classification of VIRUSClassification of VIRUS
Viruses are classifying into 3 typesViruses are classifying into 3 types
Trojan HorseTrojan Horse
WormWorm
MacroMacro

9. Trojan HorseTrojan Horse
Works of Trojan HorseWorks of Trojan Horse
 Covert
 Leaks information
 Usually does not reproduce
 Requires Windows to work
 Similar to PC Anywhere, Carbon Copy software
 Allows remote access and control of other computers
 Install a reference in the registry
 Once infected, runs in the background

10. WormsWorms
 It is similar to a virus in design.It is similar to a virus in design.
 It is considered to be a sub class of a virus.It is considered to be a sub class of a virus.
 It spreads from computer to computer withoutIt spreads from computer to computer without
any one’s help.any one’s help.
 If your computer sending out a single worm, itIf your computer sending out a single worm, it
could send thousands of copies itself.could send thousands of copies itself.
 First worm released on the Internet was calledFirst worm released on the Internet was called
Morris worm.Morris worm.
 It was released on Nov 2, 1988.It was released on Nov 2, 1988.
it was released on Nov 2, 1988.

11. MacroMacro
 Macro Viruses are imbedded in a spreadsheet or word-processor document.Macro Viruses are imbedded in a spreadsheet or word-processor document.
 When the document is opened the macro virus does its work.When the document is opened the macro virus does its work.
 Specific to certain applicationsSpecific to certain applications
 Comprise a high percentage of the virusesComprise a high percentage of the viruses
 Usually made in WordBasic and Visual Basic for Applications (VBA)Usually made in WordBasic and Visual Basic for Applications (VBA)
 The first macro virus, on a CD ROM called "Windows 95 SoftwareThe first macro virus, on a CD ROM called "Windows 95 Software Compatibility Test"Compatibility Test"
in 1995in 1995
 If you receive email that looks like the above, you have the potential to becomeIf you receive email that looks like the above, you have the potential to become
infected.infected. You won’t become infected if you DO NOT open the attachment.You won’t become infected if you DO NOT open the attachment. It mayIt may
be from someone you know. But they don't know they sent it. The subject line willbe from someone you know. But they don't know they sent it. The subject line will
read, "read, "Important Message FromImportant Message From" and the name may be someone you know." and the name may be someone you know.
 The body of the mail will read, "The body of the mail will read, "Here is that document you asked for don't showHere is that document you asked for don't show
anyone else ;-)anyone else ;-)""
 The attachment, where this nasty little bug lives, has the name ofThe attachment, where this nasty little bug lives, has the name of list.doclist.doc..
 The virus doesn't appear to cause any damage to infected computers except in rareThe virus doesn't appear to cause any damage to infected computers except in rare
cases when the minutes of the current time match the date--for example at 4:26 p.m.cases when the minutes of the current time match the date--for example at 4:26 p.m.
on March 26. In this instance, the virus will insert the Bart Simpson quotation,on March 26. In this instance, the virus will insert the Bart Simpson quotation,
""Twenty-two points, plus triple-word-score, plus fifty points for using all myTwenty-two points, plus triple-word-score, plus fifty points for using all my
letters. Game's over. I'm outta hereletters. Game's over. I'm outta here" into a user's active document." into a user's active document.

12. How virus spreadHow virus spread
Viruses spread when we execute a program thatViruses spread when we execute a program that
contains a virus code.contains a virus code.
When there is a try to boot the file from an infectedWhen there is a try to boot the file from an infected
floppy disk containing boot sector virus.floppy disk containing boot sector virus.
Viruses spread when users share infected files andViruses spread when users share infected files and
diskette and infected documents as email attachment.diskette and infected documents as email attachment.
When PCs have been connected together to form aWhen PCs have been connected together to form a
network, the damage can be worse, because the virusnetwork, the damage can be worse, because the virus
program spreads one PC to another, thus infecting allprogram spreads one PC to another, thus infecting all
the work stations.the work stations.
Viruses spread only through illegal unlicensed, piratedViruses spread only through illegal unlicensed, pirated
software.software.

13. Activities of a VIRUSActivities of a VIRUS
 The first and the foremost objective of a typical virus is to replicateThe first and the foremost objective of a typical virus is to replicate
itself and hence to spread to as many programs as possible.itself and hence to spread to as many programs as possible.
 Another important objective of a virus is to destroy the data orAnother important objective of a virus is to destroy the data or
program in the computer by overwriting parts of data or program orprogram in the computer by overwriting parts of data or program or
by simply erasing them.by simply erasing them.
 Other objectives of virus are to cause some sort of malfunctioning ofOther objectives of virus are to cause some sort of malfunctioning of
the computer system.the computer system.
 The virus can cause the malfunctioning of the computer in a numberThe virus can cause the malfunctioning of the computer in a number
of ways and it differs from virus to virus. The malfunctioning causeof ways and it differs from virus to virus. The malfunctioning cause
could be:could be:
 To disorganize the data program (deletion of the file Allocation table)To disorganize the data program (deletion of the file Allocation table)
 To decrease the memory (Space in which the computer works) and alsoTo decrease the memory (Space in which the computer works) and also
decrease the storage space of computer.decrease the storage space of computer.
 To cause storage movement and patterns of the screen, there making itTo cause storage movement and patterns of the screen, there making it
impossible to work on the machine.impossible to work on the machine.

14. Symptoms of VIRUS AttackSymptoms of VIRUS Attack
Programs take longer to load than normal.Programs take longer to load than normal.
Computer's hard drive constantly runs out of free space.Computer's hard drive constantly runs out of free space.
The floppy disk drive or hard drive runs when you are not using it.The floppy disk drive or hard drive runs when you are not using it.
New files keep appearing on the system and you don't know where they came from.New files keep appearing on the system and you don't know where they came from.
Dramatic decrease in the speed of the system. This may be either due to an increaseDramatic decrease in the speed of the system. This may be either due to an increase
in the time taken to access floppy diskette or due to virus execution itself between thein the time taken to access floppy diskette or due to virus execution itself between the
programs.programs.
Appearance of certain strange messages or strange pattern on the screen. It shouldAppearance of certain strange messages or strange pattern on the screen. It should
however be noted that this can also happen due to some other reasons as well. If it ishowever be noted that this can also happen due to some other reasons as well. If it is
due to any virus then the virus should be ascertained using some virus detectingdue to any virus then the virus should be ascertained using some virus detecting
software.software.
Strange sounds or beeping noises come from the computer or keyboard.Strange sounds or beeping noises come from the computer or keyboard.
Strange graphics are displayed on your computer monitor.Strange graphics are displayed on your computer monitor.
Files have strange names you don't recognize.Files have strange names you don't recognize.
Unable to access the hard drive when booting from the floppy drive.Unable to access the hard drive when booting from the floppy drive.
Program sizes keep changing.Program sizes keep changing.
Conventional memory is less than it used to be and you can't explain it.Conventional memory is less than it used to be and you can't explain it.
Programs act erratically.Programs act erratically.

15. Effects of a VIRUSEffects of a VIRUS
Corrupting files.Corrupting files.
Increasing file sizes.Increasing file sizes.
Interference with the display on the VDU.Interference with the display on the VDU.
Formatting the hard disk, thus destroying data.Formatting the hard disk, thus destroying data.
Marking good sectors as bad.Marking good sectors as bad.
Destroying contents of some sectors at random.Destroying contents of some sectors at random.
Slowing down the system.Slowing down the system.
Scrambling file names by manipulating the directory contents; theScrambling file names by manipulating the directory contents; the
data is all there, but the user is unable to access it.data is all there, but the user is unable to access it.
Changing all file names to a single name.Changing all file names to a single name.
Deleting the system files or renaming the system files makes theDeleting the system files or renaming the system files makes the
system hung.system hung.

16. Prevention of VIRUS AttackPrevention of VIRUS Attack
The following steps should be taken to prevent the entry of virus in to a machineThe following steps should be taken to prevent the entry of virus in to a machine
Avoid booting the machine with a floppy i.e. from “A” drive.Avoid booting the machine with a floppy i.e. from “A” drive.
If it is required to boot from floppy use a known floppy that is virus free and with aIf it is required to boot from floppy use a known floppy that is virus free and with a
write-protect. This avoids accidental infection of the floppy. Never use unknownwrite-protect. This avoids accidental infection of the floppy. Never use unknown
bootable disk.bootable disk.
Write-protect the disk while using it on unknown machines. No virus can infect aWrite-protect the disk while using it on unknown machines. No virus can infect a
floppy that is write-protected. The floppy disk controller and drive mechanism of afloppy that is write-protected. The floppy disk controller and drive mechanism of a
properly working disk drive does not allow to write onto a write-protected floppy.properly working disk drive does not allow to write onto a write-protected floppy.
Never use software that is not original or doe not come from an authorized dealer.Never use software that is not original or doe not come from an authorized dealer.
The chances that the pirated software may be infected are quite fair.The chances that the pirated software may be infected are quite fair.
If it is necessary to use borrowed software (as long as it is not illegal) scan it for beingIf it is necessary to use borrowed software (as long as it is not illegal) scan it for being
virus free.virus free.
Do not trust blind attachments.Do not trust blind attachments.
Do not open unexpected attachments.Do not open unexpected attachments.
Do not assume email received is not infected, especially when it comes from someDo not assume email received is not infected, especially when it comes from some
one known-that person might be infected without being aware of it.one known-that person might be infected without being aware of it.
Educate your self about how to update antivirus software.Educate your self about how to update antivirus software.
Apart from the above precaution, we can also use some watch dog programs whichApart from the above precaution, we can also use some watch dog programs which
monitor the system activity and prompt the user in case a virus tries to enter themonitor the system activity and prompt the user in case a virus tries to enter the
system.system.

17. REMOVING THE VIRUSREMOVING THE VIRUS
When the virus is found /detected, the next stage is to clean the virus throughWhen the virus is found /detected, the next stage is to clean the virus through
antivirus. There are many antivirus availed in market to detect andantivirus. There are many antivirus availed in market to detect and
clean viruses.clean viruses.
Antivirus:Antivirus:
The Antivirus software is used to scan and remove viruses. To protect theThe Antivirus software is used to scan and remove viruses. To protect the
system from the dangerous virus, one should keep any antivirus software insystem from the dangerous virus, one should keep any antivirus software in
the system. It always takes care of the virus and when a virus intends tothe system. It always takes care of the virus and when a virus intends to
enter the system, the antivirus activates and alerts the user about the virus. Itenter the system, the antivirus activates and alerts the user about the virus. It
asks the user either to remove or repair the virus.asks the user either to remove or repair the virus.
There are much antivirus software that are currently available in the market.There are much antivirus software that are currently available in the market.
Norton AntivirusNorton Antivirus
AVGAVG
PC CILINPC CILIN
McAfee.McAfee.
Nashot.Nashot.
Smartdog.Smartdog.
AvastAvast
Vaccine.Vaccine.
Quick HealQuick Heal