Avoid AV software and use LUA + SRP ... been running for over seven years on friends and families machines virus free.
http://www.mechbgon.com/srp/
how do you know there ain't any malware on it?
Comparing .exe hash
SRP is effective but most average users would get frustrated if something didn't launch, install, or uninstall and wouldn't know what to do besides bitch and complain.
Comparing .exe hash
Good idea. Have you ever heard of rootkits? They sort of encrypted these days.