1999/9/13
The famous paper by Ken Thompson (the creator of the original UNIX), in which he describes his infamous self-perpetuating C compiler/login trojan horse.
The moral is obvious. You can't trust code that you did not totally create yourself... No amount of source-level verification or scrutiny will protect you from using untrusted code... As the level of program gets lower, these bugs will be harder and harder to detect. A well installed microcode bug will be almost impossible to detect.