Disable all your WordPress core updates on plugin activation.

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 core updates as well as notifications for the same. It will prevent your WordPress to check for new updates. This plugin is ideal for whom who have customized and enable theme / plugins to work with existing WordPress verstion and won’t break site at time of WordPress core update.
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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