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 = ; i < hdids.Count; i++)

             { num += hdids[i].ToString().Replace(" ", ""); }

             return num;

         }