The magic words being "Secure Attention Key" (on multics in particular, it was specifically caught by the Front End Processor, so nothing in the OS could interf

The magic words being "Secure Attention Key" (on multics in particular, it was specifically caught by the Front End Processor, so nothing in the OS could interfere by (for example) catching the signal and printing a fake login prompt, becauase it was literally a separate computer handling the request...)