Secure attention key
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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, 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, which is the part of the operating system that interacts directly with the hardware, can detect whether the secure attention key has been pressed. Though third party application programs cannot intercept such a key, rootkit viruses gain administrative access to the target computer, could modify the operating system and could thus obtain control of the secure attention key of the affected system.
The secure attention key is used to make login spoofing more difficult.