The most disastrous software bugs in history
The top 3 according to 98 votes from people: Therac-25 (1985–1987) · The Patriot missile at Dhahran (1991) · The Pentium FDIV bug (1994). (Updated Mar 6, 2025.)
A rocket that blows up after 37 seconds, a probe lost by mixing up units, 440 million dollars gone in 45 minutes… Software failures that cost fortunes and, sometimes, lives. Which is the worst?
Automatically translated (original in Español). See the original
Top 13
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1
Therac-25 (1985–1987)
A radiation therapy machine gave several patients lethal overdoses.
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2
The Patriot missile at Dhahran (1991)
A rounding error in its clock let through a Scud that killed 28 soldiers.
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3
The Pentium FDIV bug (1994)
A table error made some divisions wrong; Intel spent $475 million on the recall.
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4
Knight Capital (2012)
Old code reactivated by mistake lost 440 million dollars in 45 minutes.
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5
Toyota's unintended acceleration (2005–2010)
Millions of cars recalled around the world.
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6
The AT&T long-distance outage (1990)
Nine hours without long-distance calls in the United States.
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7
The Ariane 5 rocket (1996)
It exploded 37 seconds after lift-off because of an overflow in code inherited from Ariane 4.
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8
The Healthcare.gov launch (2013)
The US health insurance website managed only six sign-ups on its first day.
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9
The UK Post Office Horizon system (2000–2014)
Its false shortfalls led to more than 700 innocent sub-postmasters being prosecuted.
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10
The Amazon S3 outage (2017)
A mistyped command took half the internet offline for hours.
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11
The FAA NOTAM system (2023)
It grounded every flight in the United States: more than 1,300 cancellations.
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12
Bank of Ireland's ATMs (2023)
A glitch let customers withdraw money they did not have, and queues formed at ATMs.
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13
Mars Climate Orbiter (1999)
One team used metric units and another imperial: the probe disintegrated at Mars.
How is this ranking ordered? By people's votes: each ▲ adds a point and each ▼ takes one away. Anyone can vote and add what is missing.
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