[TECK]

Yes they do. Is in vBulletin options. But I don't recommend to anyone to use it, since it ads queries. That's no good, IMO.
The best way to make a forum private is this (I use it on my board):

Make sure your access masks are OFF:
vBulletin Options > User and registration options > Enable Access Masks? > No

Also, make sure you forum is not set as "private" (for mods and admins):
Forums & Moderators > Modify > Your Private Forum [edit]
Private forum
(Invisible to all except moderators and admins; user access masks must be on!)
Set it to NO.

Once done, do this:
Forums & Moderators > Permissions > Your Private Forum
(COPPA) Users Awaiting Moderation [edit] > Click on [edit]
Select "Use custom settings" > Set to "No" all options > Save Settings

Repeat this step for every group you don't want them to have access to your forum.

Your board will run alot faster and your threads will be hidden.
Let me know if you got any other questions.