Questo mi ha già chiarito parecchie cose:

By default, there are three desktops in the interactive window station: default, Winlogon, and screen-saver. The default desktop is created when the logged-on user starts a process. It is the active desktop, and it is used to interact with the user. If you press the CTRL+ALT+DEL key sequence, you are switched to the Winlogon desktop. Whenever the screen saver activates, you are automatically switched to the screen-saver desktop, which protects the processes on the default desktop from unauthorized users. Unsecured screen savers run on Winsta0\default.