I have mine set so that no one can see anything without logging in, look here and see if that is what you want:
www.srmcpharmacy.com.
To do that go to your Usergroup manager and edit the Unregistered/Not logged in group. Set the option under "View forum" to no...or whatever combination of options you would like. You can edit the message that appears by searching in phrases and changing it to whatever you would like it to say.