Between June 1985 and January 1987, Therac-25, a medical accelerator used for radiation therapy, was involved in six mass overdose accidents. Many patients die; others are seriously injured. The machine designed to heal becomes the focus of an investigation into the security of computerized systems.
Nancy Leveson and Clark Turner study this series in an investigation published in 1993. Their work examines the factors related to the software, but also the reactions of users, the manufacturer and the authorities. The case therefore does not amount to a typo committed in front of a screen.
The interface commanded a physical action on a person. Seemingly normal operations were not enough to demonstrate the safety of processing: rare failures also had to be examined.
The Therac-25 remains a case study in computer security. The software needed to be reviewed with hardware protections, reported incidents, and people exposed.
What we know
The story is about documented accidents from 1985 to 1987, not about current devices.
To go to the source
References accessed October 11, 2026. Linked pages may be in another language.
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