Heard of message only windows? These windows are not visible, non enumerable. Here is something from MSDN on these windows!
“A message-only window enables you to send and receive messages. It is not visible, has no Z order, cannot be enumerated, and does not receive broadcast messages. The window simply dispatches messages.
To create a message-only window, specify the HWND_MESSAGE constant or a handle to an existing message-only window in the hWndParent parameter of the CreateWindowEx function. You can also change an existing window to a message-only window by specifying HWND_MESSAGE in the hWndNewParent parameter of the SetParent function.
To find message-only windows, specify HWND_MESSAGE in the hwndParent parameter of the FindWindowEx function. In addition, FindWindowEx searches message-only windows as well as top-level windows if both the hwndParent and hwndChildAfter parameters are NULL.”