So you have followed everything in the following, and are still having issues?
First you need to follow our advisory about deleting the install folder off your forums.
Then please read the following two blog posts:
http://www.vbulletin.com/forum/blogs...ve-been-hacked
http://www.vbulletin.com/forum/blogs...vbulletin-site
Also please see these recent security announcements:
vBulletin 4.1.x-4.2.x & All versions of vBulletin 5:
http://www.vbulletin.com/forum/forum...-1-vbulletin-5
vBulletin 5.0.x patch released, for a different security issue:
http://www.vbulletin.com/forum/forum...d-all-versions