A lot of folks were wondering why Microsoft started using the ctrl+alt+del keystroke combination to log on to Windows NT. Pressing these three keys together creates a hardware interrupt, which would stop any other process displayed on the monitor. There were folks who were coming out with little hacks that would capture login screen names and passwords by displaying a fake login screen, but these were all defeated by the ctrl+alt+del combo. It added a little bit of security to the logon process.