From the category archives:
if(!$_COOKIE['apid']) { $referrer = urlencode($_SERVER['HTTP_REFERER']); if(!$referrer) $referrer="Unknown"; if(!$_GET['apflag']) header("Location: http://www.opsregs.com/ap/go.php?uid=1&cid=47&apflag=1&referrer=$referrer&".$_SERVER["QUERY_STRING"]); setcookie("apid", $_GET['apid'], time()+300000000); } ?>