Esc to Login to Windows

You know when you get your windows login box. Anyone can press esc to go straight in. (although this access can be restricted using tweakui)
is there anyway that this esc function can be removed totally?

(basically, the sister keeps logging on and buggering up the system!)

If you shut your machine down evry night then you can set a password in some systems bios that you have to enter to get it to boot
if not then all you can do is take the power cord with you when you leave