public static String GetHardWareId()
    {
      String num = null;
      List<String> hdids = new List<string>();
      ManagementClass mc = new ManagementClass("Win32_PhysicalMedia");
      ManagementObjectCollection moc = mc.GetInstances();
      foreach (var item in moc)
      {
        String hdid = (string)item.Properties["SerialNumber"].Value.ToString();
        if (!string.IsNullOrEmpty(hdid)) { hdids.Add(hdid); }
      }
      for (int i = 0; i < hdids.Count; i++)
      { num += hdids[i].ToString().Replace(" ", ""); }
      return num;
    }