public static function convertVisitorIdToBin($id)
    {
        if (strlen($id) !== Tracker::LENGTH_HEX_ID_STRING
            || @bin2hex(self::hex2bin($id)) != $id
        ) {
            throw new Exception("visitorId is expected to be a " . Tracker::LENGTH_HEX_ID_STRING . " hex char string");
        }

        return self::hex2bin($id);
    }