I tried different kinds of AV tool. I would say any AV tool you choose in the market will do something for you, however they all miss some virus, especially the new emerging type. For a better protection, I would recommend to install a well known AV tool plus some special protection tool. For example, I installed both Panda AV and http://www.wenpoint.com/HiddenFinder in my Win XP. Panda can kill most known virus, and HiddenFinder can kill the hidden virus and spyware.