Actually, the RIAA and MPAA have been pushing for legislation to allow them to do just that - upload viruses-infected files, hack, and other potentially harmful activities to punish warez users. I donot believe this has been actually allowed yet, but it would basically make it legal for these organizations to "sabotage" files on or break into p2p networks in order to protect their copyrights. It is sad and, to be brutally honest, a failure on both sides (but in no way condoning theft of copyrighted materials).