Two keystrokes too fast. A status message no one understood: “Malfunction 54.” And in seconds, a patient received a lethal radiation dose. The Therac-25 wasn’t science fiction—it was a real medical device whose software failures caused at least six massive overdoses between 1985 and 1987.

This talk dissects the exact engineering mistakes that let a race condition, cryptic UX, and misplaced trust in software-only “interlocks” turn life-saving equipment into a weapon—and translates them into hard, modern lessons you can apply today. We’ll walk through how concurrency bugs slipped past testing, how reused code and optimistic assumptions compounded risk, why safety must be layered (not just “handled in software”), and how to design alarms, logs, and operator workflows that actually prevent harm.