There are two anti-spyware tools that are free that I recommend all Windows users install:
Both of these tools are free, however, you need to be diligent in terms of updating their “definitions” regularly (part of the price of using “freeware” tools).
I usually go to one of my favorite Windows program sites called MajorGeeks to get the latest versions of Shareware/Commercial/Freeware programs. I have linked the two programs above to their associated listings on MajorGeeks (if the links do not work, just go to MajorGeeks and search for those programs).
Hope that helps!