Disabling Guest Posting
From Acenet Knowledgebase
This demo will show you how to disable guest posting in PHPBB3.
[1] Log into your PHPBB3 administration control panel
[2] Click on the "USERS AND GROUPS" tab at the top of the screen
[3] Click on the "Groups' forum permissions" link on the left side of the screen under the "GROUPS" section
[4] Select 'Guests" from the "Look up usergroup" drop down and click the "Submit" button
[5] Check mark the box labeled "All forums" and click the "Submit" button
[6] Make sure all of the "Role" drop downs are set to "Read Only Access"
[7] Click the "Apply all permissions" button to finish disabling guest posting