Bit-torrent itself is not illegal. It can and is used to distribute many perfectly legal files. The illegal part is stealing software you have not paid for. It is exactly the same as walking into a store and stealing the software off the shelf.
bit-torrent is not a crime, you should use wikipedia and read some about it. the system is a very useful tool for moving files. its used alot in linux to download large files, because it automates the downloading from multiple sources. it can be used to further illegal objectives, but so can most anything.