I would ban them if I knew WHO they were. The only way I can figure is to know who read which topics and compare it to obvious information leaks. We are talking about a few hundred users on the same team. It's easy to spy, the spy might even be on our team.
The game is a long running strategy game with no short-term end.
Obviously this is a slipperly slope if not kept in perspective. I wouldn't just ban people because they read a topic I know for a fact was leaked (sometimes they taunt us by sending us a copy of our own plans verbatim, so we know for sure that there was a spy).
So... I guess the whole point is... it isn't about deleting spies. I can do that. It's about trying to find them.
Thanks for the posts, guys. The "Who Viewed This Topic" is perfect. That mixed with some IP loggers... and I think I'm set with some help at least.