General virus information
A computer virus is a parasitic program written intentionally to enter a computer without the user's permission or knowledge. The word parasitic is used because a virus attaches to files or boot sectors and replicates itself, thus continuing to spread. Though some viruses do little but replicate, others can cause serious damage or affect program and system performance. A virus should never be assumed harmless and left on a system.
For information on how to protect and diagnose computer virus issues, check the ITS Virus FAQ site.