Yes, if warrented, T-Nation would have to divulge all names, pm's/ correspondence, and IP addresses. And just because you erase you pm's that doesn't make you safe.
Discussing sources on a board isn't that smart at all, and the attitude of 'what would they want with little ol' me?" doesn't play, as there are lots of law enforcement officials out there eager to make a name for themselves, and you are just another knotch on their belt.
Protect yourself and protect your sources. Save discussions of these only for in person and encrypted (preferably) email.