[joelbugarini]

Mick (OP) responds to this assumption in the Quora comments:

I just read that. This guy certainly wasn't Ken Thompson. But this happened to me in 1991, seven years after the date of publication you posted, and the "login" portion did the exact same thing Ken was describing as far as the secret password. This was probably Thompson's genius idea implemented by the grad student. The mechanism was very different though in the compiler, but the outcome was still a poisoned compiler.

I had heard of self-modifying compiler before, too or I probably wouldn't have thought to look there myself. I'm not surprised to see Thompson behind the original idea.

[anon4]

I don't doubt the story's plausibility, but I'm left wondering how the student could have replaced the compiler with his own. Usually you need root in order to mess around with the system like that.

[keithpeter]

I thought of the 'trusting trust' paper just as I reached the paragraph about the compiler.

As an ex-PHB rather than a programmer, I think perhaps that Dr Phelps could have had taken a bit more interest in the project &c. Perhaps had a look at the code now and again as simply asked "why does this look so unlike other people's code?". Might have sent a shot across the bows of the bad apple.

[Drdrdrq]

This. I wonder what made the graduate so angry to go to such extreme lengths to protect his code. And why nobody noticed it - did they even have the right to fix the code?