How do I force the Task Manager window closed whenever it opens?

A customer wanted to close (or at least hide) the Task Manager
window whenever it opens.
They did so by setting a timer and periodically running this code:

void FindAndCloseTaskManager()

{

  HWND taskManagerWindow = FindWindow(nullptr, "Windows Task Manager");

  if (taskManagerWindow) {

    PostMessage(taskManagerWindow, WM_CLOSE, 0, 0);

  }

}

This code worked on Windows 7,
but stopped working on Windows 8.

Well, yeah, because you're searching for a window by name.
The name of the Task Manager window in Windows 7 was
Windows Task Manager:

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On the other hand, in Windows 8, the window was named
simply
Task Manager.

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And of course, those names apply only to English.
If the user's UI language is German, the name will be
Task-Manager with a hyphen.

Whether a user can or cannot run Task Manager
is an administrative decision,
not an application decision.
Use the "Remove Task Manager" group policy.

Bonus chatter:
Note that if this customer had their way,
the name of Task Manager would be a compatibility
constraint.

Bonus bonus chatter:
Don't think you can rely on the window class name either.

That is also subject to change.