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The Therac-25 was designed as a machine controlled by a computer, with some safety mechanisms switched from hardware to software as a result. AECL decided not to duplicate some safety mechanisms, and reused modules and code routines from the Therac-20 for the Therac-25.
A software bug is a design defect in computer software. A computer program with many or serious bugs may be described as buggy . The effects of a software bug range from minor (such as a misspelled word in the user interface ) to severe (such as frequent crashing ).
A related cause of accidents is failure of control software, as in the cases involving the Therac-25 medical radiotherapy equipment: the elimination of a hardware safety interlock in a new design model exposed a previously undetected bug in the control software, which could have led to patients receiving massive overdoses under a specific set ...
There have been numerous criticality accidents dating back to atomic testing during World War II, while computer-controlled radiation therapy machines such as Therac-25 played a major part in radiotherapy accidents. The latter of the two is caused by the failure of equipment software used to monitor the radiational dose given.
Such incidents would not have been an issue in a single-use machine and unlike previous models, the Therac-25 relied on software rather than hardware safety interlocks. What happened was the operator using a keypad would select a particular mode. The machine would then start a programmed cycle and move plates into position.
Between 1985 and 1987, a series of design flaws in AECL's Therac-25 medical accelerator caused massive overdoses of radiation [18] on 6 different occasions, resulting in five deaths. In 1987 the machine was found defective by the Food and Drug Administration (FDA) and eventually recalled by AECL despite their multiple denials that the problems ...
The DAO bug. On June 17, 2016, the DAO was subjected to an attack exploiting a combination of vulnerabilities, including the one concerning recursive calls, that resulted in the transfer of 3.6 million Ether – around a third of the 11.5 million Ether that had been committed to The DAO – valued at the time at around $50M.
Software has played a role in many high-profile disasters: Ariane flight V88; Mars Climate Orbiter; TAURUS — UK share settlement system and dematerialized central share depository; Therac-25 — A radiation therapy machine responsible for six overdoses due to faulty software; Failure at Dharan — Patriot Missile clock issue