protected function get_valid_hosts_options() {
        global $CFG;
        require_once($CFG->dirroot.'/mnet/service/enrol/locallib.php');

        $service = mnetservice_enrol::get_instance();

        $subscribers = $service->get_remote_subscribers();
        $hosts = array(0 => get_string('remotesubscribersall', 'enrol_mnet'));
        foreach ($subscribers as $hostid => $subscriber) {
            $hosts[$hostid] = $subscriber->appname.': '.$subscriber->hostname.' ('.$subscriber->hosturl.')';
        }
        return $hosts;
    }