2011-03-30, 11:30 PM
If your lucky, You host may provide daily backups of your account, If so, ask them to restore your account to a time that your forum wasn't hacked...
Once this is done, access your websites logs, and see how your website was hacked, and try to patch it.
Once this is done, access your websites logs, and see how your website was hacked, and try to patch it.