This is a generic description of a type of virus, which includes such notables as Klez, Nimda and Badtrans... What you have will determine how you fix it.
One thing you can try without buying anything is
Housecall from www.antivirus.com. This appears to be a pretty decent on-line virus scanner. It's what I call a post-mortem detector -- it won't protect you from getting the next virus, but it will tell you if you've got one whenever you run it. It takes awhile to download the program the first time, but after that it only requires the dat file update. It may or may not be able to clean your particular virus, but when it detects exactly which one you have, it'll also give you a link to instructions for manual removal.
Good luck!
EDIT*** I forgot to mention
AVG from www.grisoft.com. This is a free antivirus package. Seems to be pretty decent, too ... and it runs all the time, so it'll catch 'em before they become a problem.
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