UBB.Developers Forums UBB.threads 7 Development How Do I? Post Flooding

I thought this problem was fixed yet my board was subjected to an attack yesterday of someone making mass threads under any nickname he chose. It could have been a lot worse if someone would have done a little more scripting to make random usernames/subjects/messages but it was a basic script and they didn't do it for very long. I somewhat stopped them because they were coming from the same IP but it didn't seem that the ban on the IP in the admin section worked. I just hardcoded the IP into addpost.php I thought that this line was supposed to prevent this:

// Make sure this isn't being called via GET
if ($GLOBALS[REQUEST_METHOD] == "GET") {
exit;
}

Any ideas how this would be possible to stop? I'm using PHP version 5.4.2