Spybot – S&D is one of the first Anti-Spyware softwares that work effectively. Best of all, it is a free software with no string attached. Even though it is free, users can make donations to the developers through Spybot or through the website.

Spybot – Search & Destroy supports most Windows OS.

Get it here:
http://www.safer-networking.org/en/spybotsd/index.html