I had that problem, untill I tried to get rid of another one, raze spyware...
I used HijackThis, which I think is better, because it shows all things running that might be this type of shit... Although you gotta now what you should never remove..
You may have to run it in safe mode, search, and delete files like: URLSearchHook, and SearchAssistant... Also, if you find something like 180solutions, remove that one...