Avast virus definitions update 110411-1 released yesterday contained an error resulted in flagging lot of good sites as infected in browsers. Avast confirms sites with a script in a specific format (remote sites)were affected but not the local files in your Computer.
No matter you’re using free, paid and internet security suits of Avast, if you’re seeing regular browsing sites shown as bad sites Avast to blame for bogus update and they quickly released a fix after 45 minutes. Your Avast antivirus should have version number 110411-2. You can manually hit update virus definitions if Avast won’t updates definitions automatically.
Source : Avast blog