When the operating system is ready to logon with password required, or is returning from screen saver mode while password is required sometime you prefer to show or not the window which requires to press Alt+Ctrl+Del sequence first.
In order to enable or Disable this window follow these instructions:
1. Press Start -> Run...
2. Type "CONTROL USERPASSWORDS2" and press OK
3. On the opened window switch to the Advanced tab
4. Check or Uncheck the "Require users to press Alt+Ctrl+Delete"
5. Press OK