This core hook will allows to throw 404 error if user is trying to direct access the page which menu item is hidden (not active) in Admin > pages

q2am-block-direct-access.php

<?php
/*
 * hook: 		404 for non visible menu
 *
 * hook by:		Q2A Market
 * hook type: core
 * author: 		Jatin Soni
 * url:			http://www.q2amarket.com
 * version:		1.00
 * 
 * Description:
 * This core hook will allows to throw 404 error
 * if user is trying to direct access the page
 * which menu item is hidden (not active)
 *
 * usage:
 * for users page - Place below code into qa-include/qa-page-users.php
 * after $qa_content=qa_content_prepare();
 * same way you can throw 404 for other pages
 *
 * Disclaimer:
 * This program is distributed in the hope that
 * it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.
 * 
 * See the GNU General Public License for more details.
 */

if(!array_key_exists('user', $qa_content['navigation']['main'])){  

	header('HTTP/1.0 404 Not Found');
	qa_set_template('not-found');

	$qa_content=qa_content_prepare();
	$qa_content['error']=qa_lang_html('main/page_not_found');
	$qa_content['suggest_next']=qa_html_suggest_qs_tags(qa_using_tags());    	

	return $qa_content;
	
}