nasty computer viruses...

Why do people create computer viruses? You tell me and we'll both know...

from Wikipedia.com
A computer virus is a self-replicating computer program written to alter the way a computer operates, without the permission or knowledge of the user. Though the term is commonly used to refer to a range of malware, a true virus must replicate itself, and must execute itself. The later criteria is often met by a virus which replaces existing executable files with a virus-infected copy. While viruses can be intentionally destructive—destroying data, for example—some viruses are benign or merely annoying.

I've had a few computer viruses over the years and they are definitely annoying and sometimes can wreak havoc on your system, but the best way to combat the problem is to have an antivirus program running with up-to-date definitions!

Some free versions of antivirus programs are available at:
AVG Antivirus
Avast Antivirus
Avira AntiVir Antivirus