3 things to recover a cracked website.

1. Since files in the cracked website are changed, put those files back. Reinstall related software (phpBB).
2. Fix the hole, prevent other crackers to crack it again.
3. Find out what the cracker did, and prevent her from entering again.

Actually we can reinstall the php and phpBB, to do the 1st and 2nd task. Now I'm focusing on 3rd task. I don't know what the cracker did, what if she created a super-user account for herself, and she can come over anytime?