The forum was the subject of someone clearly exploiting a vunerability in phpbb, thereby wiping all of the posts and all of the forums, clearing the database.
The database has been restored from an old backup, so the majority of new posts have disappeared. You may now continue posting as normal, if you made a post and it has disappeared then you should repost it.
Note that all threads from the restored backup have been moved to the 'discussion archive' forum - this is to stop them being confused with the latest threads.
Sorry for the inconvenience!