igor0
11
First of all, I have no idea what makes you think that it’s a “known sample”.
It might be a sample avast! virus lab has never seen, and avast! 5 detects it due to more generic signatures, better unpackers, or some kind of heuristic rules.
So yes, due to reasons I just mentioned (better unpackers, code emulator, heuristics, …) - avast! 5 certainly detects more than avast! 4; you may call it a better proactive detection, thanks to architectural changes in the virus database done between versions 4 and 5. Yes, I suppose these samples are added into avast! 4 as well, but it takes some time - it’s simply “faster” if avast! 5 detects it beforehand, without having seen that particular sample.