Do you have PHPMyAdmin installed on your site? If so do you have it in a secure folder / directory requiring a user name and password to enter that directory?
Many times I see message boards "hacked", the proper term would be cracked, and destroyed and this is the case or something similar. A "hacker", proper term would be cracker, will never reveal how he got in or mess with that avenue over going after your most popular part of your site, your interactive material. He or she will always wish to return and enter back through that area once you have spent the time to restore your site and feel that you have "fixed" the problem. Them they will return once again to show you how good of a script kiddie they really are.
If you do not have full log access you most likely will never know how they got in unless you check everything for security or hire someone whom can do it for you.
