[TheLastSuperman]

When you create a new usergroup, that new usergroups is "outside" forum permissions i.e. it has not been defined as to what the new usergroup can and cannot do in forums where custom permissions are set.

As a prime example; If you create a new usergroup BUT do not redo your forum permissions AND happen to have private Admin only forums, then yes if a user is placed into this new usergroup and no forum permissions have been updated - they can and will see your private staff "Admin" forum depending on permission settings.

Usergroup permissions and Forum permissions work in conjunction with each other, they're not one in the same though.