it looks that your forum is running the latest release of phpbb 2.0.11 that is secure from the Sanity.a worm, which is taking advantage of Google to find other php/phpbb web sites to infect.This is just one part of the secure IT process. Making sure your own systems are secured and up-to-date on what software and versions are running. If every would take such an approach, a lot less harm would spread across the internet. Computing is like taking care of a car, it needs constant attention, otherwire things will go haywire...
Erik
phpbb code to fix patch http://www.phpbb.com/phpBB/viewtopic.php?t=240513