It could be a virus.
I find whenever a system's been infiltrated by spyware/viruses, I end up reformatting. Maybe it's just 'cause I'm anal and I don't believe my system will ever be clean enough after a removal, but that would be my proposed solution. Scan for viruses (
Housecall is a decent web-based scanner if you don't have the software), back up all your personal files, format, and reinstall Windows.
Just a thought...
Itchy93