I used to use AVG, but I had a virus get through a couple of seperate times. I switched to Trend Micro and haven't had any problems yet. I ran it as soon as I installed it on the computer and it found a few different spyware cookies that my other programs hadn't. It doesn't slow my computer down at all, and it only cost 40 bucks. It has anti-spyware as well, which AVG doesn't. If you do use AVG you need to get a separate anti-spyware program such as AdAware.