Ian, vBulletin is now one of the more easily hacked softwares in the www of forums. They charge the earth for patches and security upgrades and annual fees whilst hackers wander around at will. Since they were taken over by a US company they have gone worse and worse and worse.
I changed from them to IPBoard, see my pm, and am loving every second of my trouble free main forum (not the tiddler mentioned above). The older the software the easier to break into.