As They say, if a file can be put on a computer it can be found on the p2p network. .exe, .bat, .sys, .ini, .jpg, .mp3, .move and so on. So if you just download masses of, oh lets say porn. Then you are sure to get something you don't want. Same thing with music, some of it sounds like it a tape recorder and mic job. If you download masses of mp3s at once, you will also get the crap and trash. However, if you download something and don't delete it, then you will have it, and you will indirectly share it. BE CAREFUL!
In short, GET OFF YOUR SOAP BOX! It can happen to anyone! This is why I only download the songs I want. I never search for .exe (due to viruses), or .jpg (as the name can be misleading).