Disable all your WordPress updates on plugin activation that includes WordPress core, themes and plugins.

Abhay

Disable Wp Updates & Notifications

This plugin disables the themes, plugins and wordpress core updates.

gr8nilay

This plugin is use to disable all your WordPress updates as well as notifications for the same that includes WordPress core, themes and plugins. It will prevent your WordPress to check for new updates for them all. This plugin is ideal for whom who have customized WordPress / theme / plugins to work with existing WordPress version and won’t break site after updation.
Read This First: 
You need to keep your WordPress updated including themes and plugins so if you fail for the same then it will might compromise security of your site.

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