public static function getFilter()
    {
        $mobileDeviceFilterClass = eZINI::instance()->variable( 'SiteAccessSettings', 'MobileDeviceFilterClass' );

        $mobileDeviceDetectFilter = class_exists( $mobileDeviceFilterClass) ? new $mobileDeviceFilterClass : null;

        if ( $mobileDeviceDetectFilter instanceof ezpMobileDeviceDetectFilterInterface )
            return $mobileDeviceDetectFilter;

        return null;
    }