[alan92rttt]

PHP Code:

$url=parse_url($HTTP_REFERER);
if(!empty($url["host"])&&strpos($url["host"],'vbulletin.org')==0){
    echo "Error 500-invalid server call - ".$url["host"]." - Remote linking Denied";
    exit;
} 


Just change vbulletin.org to your site.

This only works of the browser is providing referer.

Then echo can be totally removed.