Marshal.ZeroFreeGlobalAllocAnsi Method

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Security;
using System.Security.Principal;
using System.Text;

namespace SecureStringExample
{

    class MarshalExample
    {


        static void Main(string[] args)
        {
            IntPtr unmanagedRef = IntPtr.Zero;

            try
            {
                // Ask the user for a password.
                Console.Write("Please enter your password:");

                SecureString passWord = GetPassword();

                Console.WriteLine("Copying and decrypting the string to unmanaged memory...");

                // Copy the Secure string to unmanaged memory (and decrypt it).
                unmanagedRef = Marshal.SecureStringToGlobalAllocAnsi(passWord);

            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
            finally
            {
                if (unmanagedRef != IntPtr.Zero)
                {
                    Console.WriteLine("Zeroing out unmanaged memory...");

                    Marshal.ZeroFreeGlobalAllocAnsi(unmanagedRef);
                }
            }

            Console.WriteLine("Done.");

            Console.ReadLine();


        }

        public static SecureString GetPassword()
        {
            SecureString password = new SecureString();

            // get the first character of the password
            ConsoleKeyInfo nextKey = Console.ReadKey(true);

            while (nextKey.Key != ConsoleKey.Enter)
            {
                if (nextKey.Key == ConsoleKey.Backspace)
                {
                    if (password.Length > 0)
                    {
                        password.RemoveAt(password.Length - 1);

                        // erase the last * as well
                        Console.Write(nextKey.KeyChar);
                        Console.Write(" ");
                        Console.Write(nextKey.KeyChar);
                    }
                }
                else
                {
                    password.AppendChar(nextKey.KeyChar);
                    Console.Write("*");
                }

                nextKey = Console.ReadKey(true);
            }

            Console.WriteLine();

            // lock the password down
            password.MakeReadOnly();
            return password;
        }
    }
}