[WordPress] Plugin or MU plugin: Sends an HTTP status of 403 when a login has failed. Idea previously published by Sergej Müller.

shoo.php

<?php
defined( 'ABSPATH' ) && function_exists( 'add_action' ) or exit;
/**
 * Plugin Name: Shoo
 * Plugin URI:  https://gist.github.com/glueckpress/3a15c8a070f9451c18e10f6d6e76c56d
 * Description: Sends an HTTP status of 403 when a login has failed. Idea previously <a href="https://plus.google.com/u/0/110569673423509816572/posts/T1gnqbiYjZZ">published by Sergej Müller</a>.
 * Version:     0.0.2
 * Author:      Caspar Hübinger
 * Author URI:  https://profiles.wordpress.org/glueckpress
 * License:     GNU General Public License v3
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */
	
add_action( 'wp_login_failed', function () {

	status_header( 403 );
} );