New Group with Hidden Status

Hello

if i have 3 Forums called

Winter
Summer
Holiday

and i make a Group called "Test"
i make this group as "HIDDEN Group" and now add 10 Members an give them the right they can "only Read" in the Forum Winter/Summer/Holiday and not Post,

Can i make the 10 Members automatic HIDDEN for all the other Users
because the dont sould be seen if they browsing the forums,
but i dont want to edit all single profils to make the status "HIDDEN" because members in the Group can make it Back to no hidden by edit the Profil.

I want to make the Members in the Group automatic Hidden forever.

Any Ideas?

Well, but if they post in the other sections they would be know.
Clear my doubts if i am mistaken.