AHA!

In order for the vBulletin team to react even more quickly to the discovery of security flaws, recent versions of vBulletin include a new system that allows the release of special security patch versions, which do nothing except fix the security problem.

This system allows a version number such as 1.0.4 to be altered to 1.0.4 PL1 (PL = Patch Level) so administrators can be sure that they are running the most up-to-date code and are no longer vulnerable to known security problems.

To make use of this system, vBulletin releases that include only security flaws will contain *only* the fixed file(s) plus a new version number file, allowing administrators to simply upload the new files without having to run an upgrade script.