This is what the hacks do.
A category is created in forum setting. The ultimatebb.cgi is edited so that it will not show that category. A second ultimatebb.cgi is created & customised so that it will only display that category.
This is what Pheonix Landing said
"They way i have written this hack is VERY SIMPLE. It works simply by creating a new Category for Private Boards. After you do this, there is a few small edits to Ultimate.cgi to filter out any board in the "Private Boards" category from showing up when displaying the main page. The second page is a duplicate of Ultimate.cgi, edited so that ONLY forums in the "Private Boards" category are displayed, then the duplicate is renamed "PrivateBoards.cgi".
Here's the code for Version 5
https://www.ubbdev.com/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=7&t=000310&p=2 At the bottom posted by InSite
[ April 14, 2001 09:30 PM: Message edited by: aaronx88 ]