GENWiki

function GoogleSafeBrowsing($url)
{
    $data = '{
      "client": {
        "clientId": "MyCompany_or_Site_name",
        "clientVersion": "1.0"
      },
      "threatInfo": {
        "threatTypes":      ["MALWARE", "SOCIAL_ENGINEERING"],
        "platformTypes":    ["ALL_PLATFORMS"],
        "threatEntryTypes": ["URL"],
        "threatEntries": [
          {"url": "'.$url.'"}
        ]
      }
    }';
    $key='YOUR API KEY';
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "https://safebrowsing.googleapis.com/v4/threatMatches:find?key=".$key);
    curl_setopt($ch, CURLOPT_TIMEOUT, 10);
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/json", 'Content-Length: ' . strlen($data)));
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
    //curl_setopt($ch, CURLOPT_VERBOSE, true);
    $curldata=curl_exec($ch);
    //$httpcode=curl_getinfo($ch,CURLINFO_HTTP_CODE);
    $response = (array) json_decode($curldata, true);
    return ($response['matches'][0]['threatType']) ? true : false;
}

Simply call GoogleSafeBrowsing('gen.net.uk'); and the function will return TRUE if listed as unsafe, otherwise FALSE. You can of course alter this to return the curl response which is either empty or has JSON data and parse it yourself for more detail.