SecureString

using(SecureString secure = new SecureString())
                {
                    secure.AppendChar('a');
                    secure.AppendChar('n');
                    secure.AppendChar('&');
                    secure.AppendChar('N');
                    secure.AppendChar('n');

                    int min = 24,max = 599;

                    for(int i = min;i < max;i += 3)
                    {
                        char c = i.ToString()[0];
                        secure.AppendChar(c);
                    }
                    string unsecure = secure.ToString();
                }