In this series, we explore the most catastrophic software bugs ever recorded, starting with the Therac-25 tragedy. Praised as a cutting-edge medical device, it turned into an instrument of harm due to a simple software bug. On March 21, 1986, a routine cancer treatment became a nightmare, resulting in severe injuries and ultimately, a tragic death. This incident serves as a important reminder of the life-or-death stakes involved in software testing in medical devices.