Yes Lynne ypu are correct. I have found this in some vbulletin forums in the past in vBulletin 3 and I would like to add i now in mine vBulletin 4 forum but I really do not know How. Only members of a group can access and view forum associated with the group.
I found this in the the site but as I am not a designer or vBulletin expert I really do not know if this applies to vBulletin 4 because this thread was created in 2008 and refers to vBulletin 3.
Code:
https://vborg.vbsupport.ru/showthread.php?t=172911