如何获取另一个进程MessageBox的消息

另一个应用程序有时显示标题为"Test"的MessageBox和MessageBox体内的一些消息，我怎么能从另一个应用程序(写在c++或c#什么)得到这个消息，然后关闭它?c#代码:

[DllImport("user32.dll", SetLastError = true)]
public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
[DllImport("user32.dll")]
public static extern int SendMessage(int hWnd,uint Msg,int wParam,int lParam);
public const int WM_SYSCOMMAND = 0x0112;
public const int SC_CLOSE = 0xF060;
for (int i = 0; i < 40; i++) // just test cycle
{
     IntPtr window = FindWindow(null, "Test");
     if (window != IntPtr.Zero) // ok we found it!
     {
          // code that reads MessageBox message?
          .....
          // work is done, closing
          SendMessage((int)window, WM_SYSCOMMAND, SC_CLOSE, 0);
          break;
     }
     System.Threading.Thread.Sleep(50);
}