File Viruses

A file virus is simply a virus which attaches itself to a program. The virus modifies the program so that when you execute the program you first run the virus then the program. This is usually done by altering the first instruction that the program executes into a 'Jump' to the virus code.

Before macro viruses were thought of there were a vast number of file viruses. If a virus writer could infect a popular shareware program then the virus could spread very quickly. Fortunately it is relatively unusual to exchange programs. Even today with the Internet very few programs are passed between people. The majority of the traffic is data.

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