Avast has a freak out, goes on a false positive spree
At first it looked like an isolated incident, but it now appears to be anything but. Avast's user forums [update] have been getting hammered for several hours by users experiencing the same thing - a rash of false positives following a recent definition update.
It's the same sort of SNAFU that went down a few months back with AVG -- which blackballed iTunes after an update. A second update quickly fixed the problem, and that will likely be the case with Avast as well.
If you use Avast and are experiencing this problem, it's wouldn't hurt to do a few manual update checks this morning to see if new bits have been made available.
update: a new .vps has been pushed, so manually update Avast if you're still having problems.