i've only seen a couple, here is the latest thread about it at SMF. i googled the hacker, EFSANE87, and seen he is registering at smf's everywhere he can find em. if your at version 1.1.4, better upgrade. you could be next.
Lol, there was a cookie session hack for the earlier versions phpbb 2. Anyone who modified the cookie could log onto the board as admin.