title: What browsers don't send HTTP_Referer
body: <p>I want to show certain content if traffic comes to my wordpress site from google search. I want to use <code>$_SERVER["HTTP_REFERER"]</code> . Security is not a huge issue -- if some client really wants to lie that they are coming thru google that is no big deal (they'll just see an ad). I also understand that I need to check what they send through <code>$_SERVER["HTTP_REFERER"]</code> for malicious code. However, I see that according to answers in this post <a href="https://stackoverflow.com/questions/165975/determining-referer-in-php">Determining Referer in PHP</a> not all browsers send HTTP_REFERER. </p>
  
  <p>What browsers don't send it? What versions?</p>