BTW - this happened before. December 2009:

“On Thursday 12.3.2009 avast! had a bad false positive issue. At around 12:15 AM GMT (4:15 PM PST) we released VPS update 091203-0 which started flagging hundreds of innocent files as a ‘Win32:Delf-MZG’ Trojan (or, in less common cases, as 'Win32:Zbot-MKK). Among the files affected were high-profile programs produced by Adobe, Realtek, sound card drivers, various media players etc.” - A VPS update 5 hours later solved it.

On April 2011, a VPS update was causing WebShield to report widespread viruses on random websites. Was fixed 5 hours later with a new VPS update.

Again in March 2013 - Avast accidentally flagged Adobe Acrobat as a virus and killed the software for many users - fortunately a repair of the Acrobat software resolved it after a VPS update (3 hour response time).