Sounds like smitfraud or vundo

Visit a antispyware website like spywareinfo or spywarewarrior. They will help you get rid of the infection.

If you feel lucky, you can search for smitfraudfix and vundofix on google

They are from atribune.org and siri.geekstogo I believe.
Either will scan for just "smitfraud" or "vundo" and clean it if found. However other infections can be present, and its advisable to seek the help of a antispyware forum to get fully clean.

A "Trademark tell-tale sign" of smitfraud is something by the name of SpyFalcon, Spysherrif, SpyQuake, etc... being in the system tray and trying to masquerade as "Windows Automatic Updates" and saying that you have an infection in your system, Windows will now download the most powerful/effective/#1 spyware solution, etc.... and after downloading, will try to get you to buy that product and send them money....