if your AV is telling you that the file has a virus DONT OPEN IT! just delete it.
other than that, there is *almost* nothing we can do about the distribution of these files because of the nature of p2p... everyone can access it. and anyone can share whatever they want.. but there is hope down the road for spam filters and a file rating system. its just going to take some time to develop and implement.
these are some upcoming features that limewire will soon have, take a look here:
http://limewire.org/wishlist.shtml
btw, limewire.org is for developers, limewire.com is for users.