Umpteen people have recommended Microsoft Security Essentials to me as a fine (and free) anti-virus program. I'm sure it must be great for some folks — maybe most folks — but I tried it after I ditched AVG and before I installed Avast, which is what I'm now running. Though it was made to work especially well under Windows 7, which is what's on my computer, MSE didn't agree with my system and things locked up during most scans. This was disappointing because I usually get along fine with Microsoft Anything, plus I like the idea of running software that has the same initials as me.
No such lockage has occurred with the free version of Avast Anti-Virus. It's so far operating unobstrusively and, it would seem, well. I will report back on any change in this condition.