if(document.cookie.indexOf("ref=") == -1 && document.referrer && document.referrer.length > 4) {
   var date = new Date();
   //Set for a month.
   date.setTime(date.getTime() + 60*60*24*30*1000);
   date = date.toGMTString();
   document.cookie = "ref="+ document.referrer + "; expires=" + date + "; path=/;";
  }