> But how do you know that it is your session? That's the whole point of a secure access key.
If somebody logged in, disabled terminate sequence and started login screen emulation, you'll notice, that nothing happens when you press Ctrl-Alt-BS. :) But I agree that "Secure Access Key" (Alt+SysRq+K on Linux) is better for that, and it works both for text and X terminals. It's just some distributions disable Magic SysRq keys, while C-A-BS usually works everywhere during login screen.