HFCS

Their "Super secret hideout for bungie.net forum moderators. Don't even try to join. You will be smited." description means that only if and when you are a Bungie.net moderator and/or employee, Forum Ninja etc. then shall you join their group.

You really don't need a link to this secret "HFCS" group because you can't have any, well... HFCS group homepage.