Avast antivirus is count as worst antivirus ever.it can remove a virus but it can delete system files that can make to reinstall windows and it can slow up the computer.
Some high Threat virus like poision IVY and agent.btz cannot remove that virus coming from internet and lag a computer.
Avast 4.6 can’t have realtime shield mode that can protect you to virus that coming from internet and also updates take too much time.
They detects trojans and worms they are regular file awast says that that was virus and simply remove it either it is system file.