Had the same problem, twice. If you use Firefox, go to tools, hit add ons, find the sucker and disable then remove it.
It didn’t show up in add ons or programs.
It was embedded in the registry.
It’s one of the really nasty buggers you can’t even find to uninstall.
That’s why I had to either pay for the SpyHunter proggy or reformat the whole machine.
I probably will reformat anyway pretty soon but it takes days to reinstall Photoshop, plugins and all that stuff and I really hate doing it.