ok heres a brain teaser then: what about the bigger files that are infested with a virus? how would you filter those out by size? any exe can contain a virus or a zip file of any size or extension. Yes, I know we need filters to search.
Remember the I Love You Virus? A simple viruses embedded in an image file that cause destruction across the web.
Trojans/worms/viruses oh my.
Nothing a P2P app can really do about them. in the end it still boils down the users that put them there. New users get hit because they dont know any better. They see a file they want and automatically down load it.
This one is easy to spot but the bigger ones arent unless you scan before downloading.