Avast free is the best free antivirus in my opinion. On my laptop in the living room, I have McAfee VirusScan Enterprise running and before, Norton Internet Security and they are running all right, but they use quite some resources. AVG is kinda mediocre in my opinion but its items fly everywhere and I had to spend a week tracking down mysterious folders when I uninstalled and I'm betting that more will fly out. Even Revo Uninstaller couldn't track down everything! I recommend Avast free for free antivirus and Bitdefender for paid for light systems and McAfee for top-notch computers with Intel i7 Haswell and at least 8 GB of RAM.