Would you like to make it so that a forum on your phpBB 2 is viewable only to logged in users? You can do this easily through the phpBB 2 permissions system. Here is how you can do it:
1. Go to your phpBB 2 admin panel. When you are logged in as an administrator on your site, you most commonly will see a "Go to Administration Panel" in the footer of your site.
2. Once inside the admin panel, in the left menu, select "Permissions" under "Forum Admin".
3. Select the forum you want to be private and click "Look up Forum".
4. The phpBB 2 permissions system has two modes. They are "Simple Mode" and "Advanced Mode." In "Simple Mode", you are presented with a single drop down menu, that includes such options as "Public", "Registered" and "Registered [Hidden]". Selecting "Registered [Hidden]" and pressing "Submit" will give you the desired result, and will allowed logged in members to create new threads, reply to threads, delete their own posts, vote in polls and create their own polls in the forum you are editing.
If you would like more control, click on "Advanced Mode" directly above the "Submit" button and you will be able to control all of the permission settings on an individual basis. For the forum to be viewable only to logged in users, you will want to set both the "View" and "Read" settings to "REG". This makes it so that only registered members can see that the forums exist and can read the topics within. You can then adjust the other settings on this page as you so please, giving different abilities to registered users, moderators and administrators. When you are finished, press "Submit".
And you are done. Do this for every forum you want to change. To test that it is working, you can log out of your phpBB and view your site as a guest.
If you have many forums and would like to change them all, in "Advanced Mode" from a single screen, you may want to install Overall Forum Permissions on One Page.