Malicious Mobile Code

Examples of DOS Viruses

There are so many kinds of DOS viruses that I often feel that mischievous minds have tried every imaginable trick. DOS viruses can infect during bootup or warm booting, across a network, when running programs, when copying files, when you scan files for computer viruses, or when you list the files on your hard drive. They have been known to use modems to dial long distance numbers when unsuspecting users left their PCs on at night. They can display elaborate graphics, sounds, and games. They can corrupt programs, data, and hardware settings. Although most virus payloads wait for a particular activation date or time, they can be computationally random or key off some other event (such as hitting Ctrl-Break). Others lie in wait for the user to unknowingly type in a particular keyword to set off some sort of damage routine. Computer viruses can taunt people and display questions the end user must answer in some twisted form of a quiz show. If you answer incorrectly, they do more damage.

The Cascade virus infects .COM files and makes the letters you were typing fall to the bottom of the screen. The Jerusalem virus infects .COM , .EXE , .BIN , .PIF , and .OVL files. It displays a “pong” black box that floats around the screen and it will delete any executables run on Friday the 13. The Flip virus horizontally flips the screen image between four and five o’clock. The Keypress bug randomly interferes with keyboard typing so that a user thinks she is continually ...