It happened back in December 2009 with Avast as well and was worse.
http://forum.avast.com/index.php?topic=51627.0
I think I read a thread around here where somebody said it was the second time it happened this year so far. Don’t know if they’re correct.
http://forum.avast.com/index.php?topic=75991.msg628545#msg628545
It happens from time to time with any AV. If it starts to get more frequent that’s when i’ll pull the plug on Avast on my own systems. Luckily with this most recent mess I didn’t quarantine anything, I just left everything alone because I knew there was something wrong.