Uhhh... Espionage _is_ part of the fun of multiframe scenarios. If your side isn't engaging in espionage, your side isn't in the game.
That said, like in the real world, the bulk of any side's intel efforts is concentrated on non-confidential sources.
Furthermore, I think both sides and the CMs agree that "espionage" does not include obtaining access to information that is password-protected.
Yet discussing in detail mission plans in a group larger than is necessary does give cause for concern. We're talking about over a hundred people on each side, and many of these people (myself included) have good friends on the other side. Now, I wouldn't willingly disclose any information; but I might let slip some detail. Now, multiply that by a hundred, and put on the other side someone with the job of collecting and evaluating that information, and suddenly discretion even in private forums becomes important.
The intelligence war is for me the most entertaining aspect of these scenarios. I've never seen a case of someone reporting information from a secure forum, but I have seen impressive results from inadvertent leaks.
