char[] chars = "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
            Random r = new Random();
            string s="";
            for (int i = 1; i <= 16; i++)
            {
                int j = r.Next(chars.Length);
                s += chars[j];
                if (i % 4 == 0 && i!=16)
                    s += "-";
            }
            MessageBox.Show(s);