Because the linked page doesn't include a description of what a Therac-25 is:
> "The Therac-25 is a computer-controlled radiation therapy machine produced by Atomic Energy of Canada Limited in 1982. The Therac-25 was involved in at least six accidents between 1985 and 1987, in which some patients were given massive overdoses of radiation. Because of concurrent programming errors (also known as race conditions), it sometimes gave its patients radiation doses that were hundreds of times greater than normal, resulting in death or serious injury. These accidents highlighted the dangers of software control of safety-critical systems."