The document discusses computer viruses and antivirus software. It defines computer viruses as malicious software that can infiltrate or damage systems without consent. It notes that viruses need a host program to spread, while worms do not. The document recommends using antivirus software and lists criteria for choosing software, including ability to detect viruses, usability, performance impact, and price. It suggests popular commercial options like KAV, Bit, and Norton but also promotes the free Vietnamese-made BKAV software as a suitable low-cost option.