Virus (computer), self-replicating computer program that interferes with a computer's hardware or operating system (the basic software that runs the computer). Viruses are designed to replicate and to elude detection. Like any other computer program, a virus must be executed to function—that is, it must be loaded from the computer's memory, and the virus's instructions must then be followed by the computer. These instructions are called the payload of the virus. The payload may disrupt or change data files, display a message, or cause the operating system to malfunction.


There are other harmful computer programs that are similar to viruses but do not both replicate and elude detection. These programs fall into three categories: Trojan horses, logic bombs, and worms. A Trojan horse appears to be something interesting and harmless, such as a game, but when it runs it may have harmful effects. A logic bomb delivers its payload when it is triggered by a specific condition, such as when a particular date or time is reached or when a combination of letters is typed. A worm only makes copies of itself, but it can take up computer memory and slow the computer's processes. (Referenced from the Microsoft Encarta Encyclopedia Online.)

A computer program that is designed to replicate itself by copying itself into the other programs stored in a computer. It may be benign or have a negative effect, such as causing a program to operate incorrectly or corrupting a computer's memory. (Referenced from www.dictionary.com)

A computer program that copies itself into the other programs stored in a computer with either a benign or negative effect.(Referenced from The American Heritage College Dictionary, Third Edition. Copyright 1997, 1993 Houghton-Mifflin Company.)

A computer program that rips your system to shreds, and sends it on to everyone else you know to rip them to shreds. You really shouldn't have run it in the first place!(This is my own definition. Like you couldn't tell.)