protected function _getUserAgentDevice($browserType)
    {
        $browserType = strtolower($browserType);
        if (isset($this->_browserTypeClass[$browserType])) {
            return $this->_browserTypeClass[$browserType];
        }

        if (isset($this->_config[$browserType])
            && isset($this->_config[$browserType]['device'])
        ) {
            $deviceConfig = $this->_config[$browserType]['device'];
            if (is_array($deviceConfig) && isset($deviceConfig['classname'])) {
                $device = (string) $deviceConfig['classname'];
                if (!class_exists($device)) {

                    throw new Zend_Http_UserAgent_Exception(sprintf(
                        'Invalid classname "%s" provided in device configuration for browser type "%s"',
                        $device,
                        $browserType
                    ));
                }
            } elseif (is_array($deviceConfig) && isset($deviceConfig['path'])) {
                $loader = $this->getPluginLoader('device');
                $path   = $deviceConfig['path'];
                $prefix = isset($deviceConfig['prefix']) ? $deviceConfig['prefix'] : 'Zend_Http_UserAgent';
                $loader->addPrefixPath($prefix, $path);

                $device = $loader->load($browserType);
            } else {
                $loader = $this->getPluginLoader('device');
                $device = $loader->load($browserType);
            }
        } else {
            $loader = $this->getPluginLoader('device');
            $device = $loader->load($browserType);
        }

        $this->_browserTypeClass[$browserType] = $device;

        return $device;
    }