I also had this problem months ago. All i did was
1) Lavasoft Anti adware program.(Clean all the adware if any)
2) Norton Anti virus.( There's some adware that can't be deleted) So i write them down.Alwasy get an error sign when delete it manually
3) Run spyboard serach and destroy(Just to make sure)
4) Lastly system restore to the earlier date
and find the file that was not deleted by Norton and delete them manually.
It's gone. I hope it's gone forever