Plugin System 
From version 3.5, vBulletin has an extensive plugin system, allowing new features to be added and functionality to be changed by third-party add-ons, without modifying the core vBulletin code.

The following sections detail some of the methods in which this can be done.
User Contributed Notes: Plugin System Add a Comment
Mike Pepper <pepper at w3pg dot com> Mar 21st '07, 11:18pm
"Plugins" are all kept in the vB database. Plugins are not autonomous php files.

Plugins are added, edited, activated, deactivated and deleted all via the "Plugin Manager" on the admin control panel ("admin cp" or "acp").
ACP -> Plugins & Products -> Plugin Manager.
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