There are a few similar topics on the Bleeping Computer forums. It appears you're not the only one with the problem, and you may want to either follow some of the advice there.
This thread seems to involve someone actually solving and removing the infection:
http://www.bleepingcomputer.com/forums/topic391685.html
I'm not sure if this will help, but some of the scanners and tools referred to in that thread may help you out.