Sounds like you've got a case of SmitFraud or something similar. AVG might be able to get rid of it, or Spybot: Search & Destroy, but that virus is quite persistent. One of the more effective ways to get rid of it is with SmitFraudFix, which can be downloaded here. Follow the detailed instructions on the web page - the process takes a while to complete. Even then, that's no guarantee. Most malware is easy to get rid of, but some of it likes to jump between networked computers and hide traces in system files only to recreate itself when its other files are deleted. If you can't get rid of it, ultimately you might need to do a fresh install of Windows.