Just saw this wee thread. It was indeed Avast! They sent out a dodgy virus definition update that was triggering false detections on many sites, many apps, and also many windows files. It was fixed with a new update approx 12hrs later. Luckily for me I chose "no action" (suspecting a bad VPS when I saw what was being detected) and my computer is not a paperweight. Others were not so lucky - there's >20 pages relating to the issue on the Avast forum. :/