if ($_SESSION['user_ip']!=$_SERVER['REMOTE_ADDR']){
  // force logout
  $_SESSION = array();
  if (ini_get("session.use_cookies")) {
    $params = session_get_cookie_params();
    setcookie(session_name(), '', time() - 42000, $params["path"], $params["domain"], $params["secure"], $params["httponly"]);
  }
  session_destroy();
  header("Location: https://lostcave.ddnss.de/common/threadr/login/?error=session");
  die();
}