Does this only apply to downloaded executable programs, or does it also apply to picture downloads - like from YouTube & picture files?
I think attachments to pics or videos would fall under "virus" rather than "trojan horse," which is what is at issue here.
However, I believe one bad-guy tactic is to trick people into downloading executables in the form of a particular "codec" that ostensibly decodes a type of video or picture file that has just been downloaded.