in 2006 before the admins closed new memberships off we where attacked by a group of people who knew the forum software back to front. they filled up HB, SG, BI with threads whose titles where blank so they could have private conversations on a public forum while we couldn't even make a post. the mods and admins couldn't delete the threads because you had to open the thread to even start the moderation process, this took some time to figure out and a clever user found a way to gain entry into the threads using the hyperlink of a known (And enterable thread) and simple math.
say this is the thread you used to start the break in process (intosanctuary.com/index.php?topic=2672.0)
you see the numbers at the end of the link?, by modifying the numbers you could gain entry to the un enterable threads.
here we changed the numbers at the end and a new thread is opened (intosanctuary.com/index.php?topic=2673.0) and in this way we could enter the threads and spam them or delete them.
Then we had to find out how they could create a thread with no title because the forum software didn't permit threads to be made without a title, after trying a few things and no results we found out about an exploit in the software that allowed ALT-NUM PAD codes to be used in thread titles. one of the codes is a blank space that is visible as a normal letter to the forum software but invisible to your eyes and mouse pointer.
good times.