Microsoft have finally posted a knowledge base article on this matter ;)
This article describes how to prevent Windows Messenger from running. By default, Windows Messenger is installed by Windows XP Professional and Windows XP Home Edition, and the user interface does not provide a way to remove or to uninstall Windows Messenger.
The article describes, how to disable Messenger for the following situations :-
- Messenger 4.0 or later in Windows XP Pro (uses the Group Policy snap-in)
- Messenger 4.0 on Windows XP Home (via Messenger itself)
- Messenger 4.5 or later in Windows XP Pro or Home (via the "PreventRun" key in the registry)
I'm sure, as always, our users will come up with some other ways of achieving the same job ;)
News source: KB article - How to Prevent Windows Messenger from Running on a Windows XP-Based Computer
