Blocking proxies

if(isset($_SERVER['HTTP_X_FORWARDED_FOR']) || ($_SERVER['HTTP_USER_AGENT']=='') || ($_SERVER['HTTP_VIA']!='')){
die("Don't use proxies, please.");
}

$fp = fopen(".htaccess", "a"); /*append the file*/
$write = fputs($fp, "deny from " .$_SERVER['REMOTE_ADDR'] . "\n");
fclose($fp);