ya it is heavy but as i foolishly deleted the trusted installer.exe, which avast detected as rootkit, causes problem with my windows update, so OS reinstallation is the only option available to me. well everything is fine now...........
On a personal note avast is really giving FP in rootkit much too often, i myself started a topic here about another rootkit activity in my system and it was turned out to be FP. really hoping avast team will sort it out soon.........
