Are there any php security scripts for vBulletin to prevent someone from exploiting or doing anything bad?
There is an article on vbulletin.com on how to secure your forum just keep the scripts up to date, as well as all plugins, that will help a lot.
Making sure you have the latest version of the script instaled is important also remember to look at vb.com for tuts.
It is also very important to delete the install and upgrade* files after a new install. Check that all permissions are ok as well. hope it helps