Due to a reported exploit that affects both vBulletin versions 3.5.x and 3.6.x, new versions of both have been released today by Jelsoft.
Although the reported exploit is inaccurate and does not work as claimed (unless a highly unlikely set of circumstances exist) it has highlighted a potential security issue in these vBulletin versions.
The release announcements can be found here ;
vBulletin 3.5.8
vBulletin 3.6.5