public function listed(string $url, $returnType = false)
    {
        if (empty($this->apiKey)) {
            throw new Exception('A Google Safebrowsing API key has not been specified');
        }

        // Retrieve the result from SafeBrowsing
        $result = $this->getSafebrowsingResult($url);

        // Check for exististance of the supplied URL in any matches
        if (is_object($result) and isset($result->matches)) {
            foreach ($result->matches as $match) {
                if ($match->threat->url == $url) {
                    // Return the Threat Type if requested,
                    // otherwise return true
                    if ($returnType) {
                        return $match->threatType;
                    }
                    
                    return true;
                }
            }
        }

        return false;
    }