A security issue has been reported to us that affects vBulletin 4. We have released new builds of vBulletin 4.2.2 and 4.2.3 to account for this vulnerability. The issue may allow attackers to access sensitive data via the mobile API. It is recommended that all users update as soon as possible. If you're using a version of vBulletin 4 older than 4.2.2, it is recommended that you upgrade to that version as soon as possible.
You can download the build for your version here: http://members.vbulletin.com/
Special thanks to NytroRST for reporting this issue.
To install the new build, download your version of vBulletin 4 (4.2.2 or 4.2.3) then upload all files found within the zip file except the /install/ directory. Make sure to overwrite the existing files on your server.
If you're using a version prior to 4.2.2, then you should follow standard upgrade procedures.
vBulletin 4.2.2 Patch Level 2
vBulletin 4.2.3 Beta 1