It takes registered users to post on this forum so im assuming its getting hit with a auto php sessions sploit script. Till or Falko call the host of this site and ask them to turn register globals on and magic qoutes off in there php.ini. You can verify if they did with a Code: <? phpinfo() ?> Then the forum will not be vulnerable to spam anymore.
We're hosting HowtoForge on our own servers. register_globals is off because otherwise it would be a security risk. I've searched vbulletin.org for anti-spam mods, but I haven't found anything acceptable yet that blocks spam and doesn't hurt real users. So we'll have to continue to delete spam manually...
Well i had the same problem with spammers on my forums, but i found this 2 mods http://www.vbulletin.org/forum/showthread.php?t=135094 & http://www.vbulletin.org/forum/showthread.php?t=134856 ... after installing them they stopped . HTH! Vlad
Both solutions are for vBulletin 3.6.x, but we're still using 3.5.4 and can't update due to some modifications we made...
Maybe you should try to modify the plugins , i don't think it's a big difference between 5.4 and 6.x .