public function isSpam(Request $request)
    {
        $spammers = $this->getSpammerListFromCache();

        $referrerUrl = $request->getParam('urlref');

        foreach ($spammers as $spammerHost) {
            if (stripos($referrerUrl, $spammerHost) !== false) {
                Common::printDebug('Referrer URL is a known spam: ' . $spammerHost);
                return true;
            }
        }

        return false;
    }