talking explicitly it is not legal to download the copyrighted materials by any means, but there are millions of users worldwide sharing copyrighted materials thru bittorrents so it's upto u if u wanna use it or not. also bittorrent technology is perfectly legal and started as means of sharing large files easily but sharing copyrighted materials w/o owner's authority is perfectly illegal. FYI one third of the total internet traffic is the bittorrent traffic these days.