People probably don't randomly rename the files. There are p2p 'poisoners' out there though, that work for the media companies, who will rename shit, or zap some of the binary data in the middle of files so they don't play, etc. That is their job, to make the process of people ripping off their customers' artistic creations via p2p (or really, any illegal means) as painful and full of hassle as they possibly can.