just wondering which hack did vbulletin.org uses for this?

[Logician]

Today at 11:56 AM CR- said this in Post #3
Does this hack affect the ability to properly upgrade vbulletin verions?

There is no hack that does not affect the ability to upgrade vbulletin versions. If a script is capable of doing it, it is called an add-on, not a hack anyway.

A hack is a modification in default vbulletin files. So when you upgrade your version, this file will be replaced with the new version's file which means that you will lose your hack as its code is overwritten with your file update.

So all hacks needs to be reapplied after version upgrades and this is how they affect the ability to upgrade vb versions.