John, you may have hit on it. Avast has become super-sensitive and detecting false positives. It said that I had a malicious infection so I spent several hours last evening trying to track it down, nada!

I read an article recently about the best free AV. Avast, as well as MS Security Essentials rated near the bottom of the pile. I didn't mention it intentionally because a lot of forumites swear by MSSE.