In 2021, a vulnerability was revealed in a system that lay at the foundation of modern computing. An attacker could force the system to execute arbitrary code. Shockingly, the vulnerable code was almost 54 years old — and there was no patch available, and no expectation that one would be forthcoming. Fortunately, that’s because the system in question was Marvin Minsky’s 1967 implementation of a Universal Turing Machine, which, despite its momentous theoretical importance for the field of computer science, had never actually been built into a real-world computer. But in the decade or so after Minsky’s design, the earliest versions of Unix and DOS came into use, and their descendants are still...