[Baron Munchausen]

Yes, any program that accesses the network has the potential to be a security risk. It depends on the individual program you are using. Some P2P programs are not well coded and a 'hacker' can sometimes exploit them to install spyware (not to mention the program itself might contain the spyware!) or get a virus into your machine. I have't heard of any problems with bittorrent yet. It's not as complex as many other P2P programs and so probably less prone to security bugs.