Tech Time Warp: Reflecting on the Ken Thompson hack

In 1983, Ken Thompson and Dennis M. Ritchie received the prestigious A.M. Turing Award for “their development of generic operating systems theory and specifically for the implementation of the UNIX operating system.” However, this look back at technology history is not about that work. Rather, it’s about Thompson’s Turing Award acceptance speech—a prescient work that contains warnings worth heeding today. Continue reading this edition of Tech Time Warp to learn more.

Thompson’s speech, which was also published in the August 1984 issue of the journal Communication of the ACM, told the story of the “Ken Thompson Hack,” an experiment Thompson ran. The hack was an early example of a supply chain attack—malicious code inserted into trusted software or hardware. Thompson had created a backdoor in the Unix login function. Calling it the “cutest program I ever wrote,” Thompson wrote a version of a C compiler that allowed him to log in to Unix while it was running—without being evident in the source code.

Of course, Thompson did not have malicious intent. He wanted to prove this could be done as a warning: “The moral is obvious. You can’t trust code that you did not totally create yourself.” He went on to critique the press for romanticizing hackers as “whiz kids,” pointing out that: “The act of breaking into a computer system has to have the same social stigma as breaking into a neighbor’s house. It should not matter that the neighbor’s door is unlocked. The press must learn that misguided use of a computer is no more amazing than drunk driving of an automobile.”

More than 40 years later, these are still wise words.

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