do not require it to nail the virus(not malware) immediately. Avast primary does NOT rely on definitions, but the viruses are very Avast aware, and will sleep in dormant mode in the temp files. I simply run CCleaner at least once a day, and Avast will never find them, because they are gone.

I've seen Avast kill many files that made a move without any definition, and I let it set in quarantine until it could be identified. I've never had a false positive that stopped my applications from working.

I also never find anything on scans with Avast because it stops them before they get on the computer.

Quite frankly - now days we need more than definition based utilities anyway. You are not going to catch todays worst malware before it does damage to your pocket book - BEWARE!