ahmetax

Ok. Then we will not get a vulnerability message from now on.
Thank you.

I found the reason. It is my fault.
In order to enhance performance of my site I had stopped wp_cron, and define it to run by the system cron in 15 minutues period.
I think that logging out is controlled by a function which is in the list of the wordpress cron.
My problem is resolved.
Thank you all.

I solved my problem.
In order to load wp-db.php there are some prerequisites in WordPress 4.0. They are as follows:

define('WPINC','public_html/wp-includes');
define('WP_USE_THEMES', false);

define('FROM_CRON',true);
wp-config.php
wp-includes/version.php
wp-includes/plugin.php
wp-includes/functions.php
wp-includes/load.php

wp-includes/wp-db.php
$wpdb = new wpdb( DB_USER, DB_PASSWORD, DB_NAME, DB_HOST);

….

FROM_CRON is used to stop loading wp-settings.php when called from the cron job. It is used in config.php as:

if ( !( defined(‘FROM_CRON’) && FROM_CRON ) ) require_once(ABSPATH . ‘wp-settings.php’);

Now I can run my script as a cron job without any problems.

ahmet aksoy

Thank you mbrsolution,
I wrote the same message to the aquoid forum also. But no reply.
Regards
Ahmet