Not sure if this works for you but have you tried:
Control Panel » Group Management » Site Permissions
Guests Group( non registered user group)
Turn off (Set to 0) for say:
Can view the Member List
Can view Member Profiles
Can email posts to others
Can use the shoutbox
Can See Extra User Info
Can see the shoutbox
Some or all of those settings may accomplish what you want.
There are other ways to limit guest access as well.
