You need to have a problem to judge it tho I had and AVG free detected a rootkit infection could not repair it but at least i was aware what i had in the system. So got an A+ from me. I am testing avast now. If i was to buy one I would buy Bitdefender security suit. It rocks and very under-rated right now.The best Anti-virus in my opinion is AVG Free. I have had AVG free for 3 years with no problem at all.