# The most disastrous software bugs in history

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?

- 98 votes · 13 items
- Mar 6, 2025 · Manuela M.
- https://even.best/en/l/3375/the-most-disastrous-software-bugs-in-history

## Top 13

1. **Therac-25 (1985–1987)** (14 · ▲14 ▼0) — A radiation therapy machine gave several patients lethal overdoses.
2. **The Patriot missile at Dhahran (1991)** (8 · ▲10 ▼2) — A rounding error in its clock let through a Scud that killed 28 soldiers.
3. **The Pentium FDIV bug (1994)** (7 · ▲8 ▼1) — A table error made some divisions wrong; Intel spent $475 million on the recall.
4. **Knight Capital (2012)** (7 · ▲7 ▼0) — Old code reactivated by mistake lost 440 million dollars in 45 minutes.
5. **Toyota's unintended acceleration (2005–2010)** (7 · ▲7 ▼0) — Millions of cars recalled around the world.
6. **The AT&T long-distance outage (1990)** (6 · ▲6 ▼0) — Nine hours without long-distance calls in the United States.
7. **The Ariane 5 rocket (1996)** (5 · ▲7 ▼2) — It exploded 37 seconds after lift-off because of an overflow in code inherited from Ariane 4.
8. **The Healthcare.gov launch (2013)** (4 · ▲5 ▼1) — The US health insurance website managed only six sign-ups on its first day.
9. **The UK Post Office Horizon system (2000–2014)** (3 · ▲5 ▼2) — Its false shortfalls led to more than 700 innocent sub-postmasters being prosecuted.
10. **The Amazon S3 outage (2017)** (3 · ▲5 ▼2) — A mistyped command took half the internet offline for hours.
11. **The FAA NOTAM system (2023)** (3 · ▲4 ▼1) — It grounded every flight in the United States: more than 1,300 cancellations.
12. **Bank of Ireland's ATMs (2023)** (3 · ▲4 ▼1) — A glitch let customers withdraw money they did not have, and queues formed at ATMs.
13. **Mars Climate Orbiter (1999)** (2 · ▲3 ▼1) — 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.