Probably a virus. Check out this thread: WARNING: Viruses on network you should be aware of!

If you can't figure it out try these sites for help:

http://www.spywarewarrior.com/index.php

http://www.castlecops.com/forums.html

http://forums.spywareinfo.com/index.php?showtopic=79038

Another good thread: Anti-virus protection and so on

and viruses, spyware, and other nasties.

Good luck.

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