when you attach the compressed (zip rar or wotever) file to the mail client, it may not check it. but when the receiver downloads it, if he has a good anti-virus program it may get detected. if it does not get detected while the file in in zip/rar format, it will definitely be detected once he extracts it. the receiver must be having a really crappy virus gaurd if that dsnt happen
best way to destroy a computer is to write your own e.g. batch file... but why waste time and destroy someone's computer?