Plugin/Hook System 
Admin Control Panel > vBulletin Options > vBulletin Options > Plugin/Hook System

Enable Plugin/Hook System (yes/no)

This setting allows you to globally enable or disable the plugin/hook system.

The plugin/hook systems allows for insertion of arbitrary code into specific locations in the PHP files without having to edit the files (see Plugin Manager). This can be used to extend the functionality of vBulletin without hacking. When upgrading to future versions you do not have to re-apply these modifications to the original vBulletin files, making upgrading an easier task.

By switching the system off, only vBulletin-native code will be run, so it can be used to establish whether errors exist within vBulletin itself or in plugin code.
Note:
You can code these plugins yourself or download existing ones from the official resource community at http://www.vBulletin.org/. Please note that these plugins are unofficial and are not supported by Jelsoft.
Warning:
If you have attempted to import a product or a plugin and run into the problem of being unable to navigate/work with your forum or control panel you might require to update the config.php file with this variable, which will force-disable the hook system. Allowing you to restore your forum and uninstall the bad code/plugin.
define('DISABLE_HOOKS', true);
(Remove from the config.php file when done.)
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