CP -> Forums -> Forum Settings -> Details -> Forum Permissions
"No Access" is the option you're looking for; which gives the group 0 access to the forum (they can't see, post, or create threads).

I'm sure that people could craft an SQL query for you to go through and update this for every forum, however I have company.

Also, I don't offer private support for non-clients, as people come by with the same questions and by keeping support private they have to ask the same question again and again

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
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