computer virus (km-pytr vrs)
n.

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 filling a computer's memory with unwanted codes.

so it MAY cause something bad

so a virus is a program that is designed to replicate its self by itself on other programs stored in the computer (or someone elses computer)



(from dictionary.com)