DEFINITION OF COMPUTER VIRUS, WORM, TROJAN HORSE: A VIRUS is a computer program that is capable of attaching to disks or other files and replicating itself repeatedly, typically without user knowledge or permission. A VIRUS is designed to spread from file to file on a single pc, it does not intentionally try to move to another pc, and it must replicate, and execute itself.

Unlike viruses WORMS do not infect other computer program files. These are parasitic computer programs and replicate by creating copies on the same computer, or they send the copies to other computers via a network.

A TROJAN HORSE is a malicious program that pretends to be a benign application. It purposefully does something the user does not expect. Trojans are not viruses since they do not replicate