I have Windows 7 installed in Boot Camp on my 2011 MacBook Pro, and I have it configured to require a Ctrl+Alt+Del to login. There's no "Del" key on the MacBook Pro. There is a "Delete" key, but that's equivalent to "Backspace" in Windows. So I have to press Fn+Delete on the MacBook Pro in order to simulate the Windows "Del" key. Pressing Ctrl+Alt+Fn+Delete works on the Windows login screen, but I noticed that Ctrl+Alt+Delete works too. That means Windows is accepting Ctrl+Alt+Backspace, and it shouldn't accept that on the login screen.