The secure attention key is a special key combination to be entered before a login screen is presented, for example Control-Alt-Delete for Windows, Control-Alt-Pause or the SysRq K sequence for Linux, or Control-X Control-R for AIX. Users should be instructed to report login prompts that appear without having pressed this key combination. Only the kernel (computer science), which is the part of the operating system that interacts directly with the hardware, can detect whether the secure attention key has been pressed, so it cannot be intercepted by third party programs.
The secure attention key is used to prevent login spoofing.