The Therac-25 software radiation disaster (en.wikipedia.org)

The Therac-25 was a computer-controlled radiation therapy machine that, after safety mechanisms were moved from hardware to software, suffered multiple incidents in the mid-1980s where software race conditions led to patients receiving massive overdoses. Across at least six documented accidents, incorrect mode selection and failures such as beam activation during “field light” setup allowed high-current electron beams to be delivered without the proper radiation target or shielding. The cases resulted in severe injuries and deaths, and the machine became a widely cited study in software reliability and safety for medical devices.