1. Run the cron by browsing to yourmoodlesite.org/admin/cron.php e.g. http://qa.moodle.net/admin/cron.php (no login required).
2. Check that no error messages are displayed.
3. Log in as an administrator, go to Settings > Site administration > Security > Site policies and tick the 'Cron execution via command line only' checkbox.
4. Try running the cron again and check that an 'internet access to this page has been disabled' message is displayed.