PHPBB is a forum script - NOT a script like MySpace...
All scripts are likely to have a few bugs, problems, and potential security risks with them. Remember, being hacked is also your responsibility, it coul have been a hole in your hosting company, or you could have simply lost your password to a worm - which means your computer is vulnerable rather than the script.
Also, remember, there are security updates and reporting procedures.
Backup, backup DB, files ect on a regular basis, when data changes ect - frequency is a decisionor you to make.
A quick search on Google would be useful:
MySpace Script [google.com]