Disable plugin updates

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<?php
remove_action( 'load-update-core.php', 'wp_update_plugins' );
add_filter( 'pre_site_transient_update_plugins', create_function( '$a', "return null;" ) );
?>

Instructions:

This snippet simply prevents WordPress from checking if there’s any updates for your plugins.

This could be useful if you’re creating a website for a client, and don’t want them to update their plugins incase you have changed the code in it, or if you’re worried that the update will break the site.