The secure attention key (SAK) is a special key combination to be entered before a login screen is presented. Examples are Control-Alt-Delete for Windows NT-based systems (called Secure Attention Sequence), Control-Alt-Pause or the SysRq-K sequence for Linux, Control-X Control-R for AIX, Break for OpenVMS or Shift-STOP for PLATO IV in the 1970s. Users should be instructed to report login prompts that appear without having pressed this key combination. Only the kernel, which is the part of the operating system that interacts directly with the hardware, can detect whether the secure attention key has been pressed.
The secure attention key is used to make login spoofing more difficult.
In Windows this is handled by the Winlogon component which calls GINA.
