Mark your calendars! September 9 is hereby declared Debugging Day. It's been associated with removing bugs for more than 50 years now but is rarely formally celebrated. So let's start the tradition this year. It all began with a log entry from 1947 by Harvard University's Mark II technical team. The now classic entry features a moth taped to the page, timestamped 15:45, with the caption "Relay #70 Panel F (moth) in relay" and the proud boast, "First actual case of bug being found."

moth taped to computer log

OK, the history of computer bugs didn't really begin on this date, but nevertheless, its anniversary seems a perfect time to examine famous bugs and other ghosts in the machine. Here is a highly selective, and therefore incomplete, collection of infamous software bugs. Unlike the relatively benign tale of the moth in the relay, some bugs have wreaked disaster, embarrassment and destruction on the world. Some have literally killed people.

Don't expect this collection to contain tales of the Ping of Death or other faults exploited by hackers and malware, such as the Spanair crash of 2008 or the possibly apocryphal tale of the CIA sabotaging the Soviet gas pipeline. Nor will it include deliberate decisions by programmers that came back to haunt them later, as with Y2K. Instead, this story is about outright programming errors that caused key failures in their own right.

Have I missed anything important? Consider this a call for nominations for the biggest bugs of all time. These are my suggestions, if you have any honourable mentions, bring 'em on. The worst anyone can do is swat them.

Space bugs

Programming errors that derail high profile space exploration missions, especially bugs that cause spectacular explosions, are frightening, expensive and career-killingly embarrassing for those who let them slip through. They provide extremely vivid reminders for all of us to check and recheck (and recheck and recheck and recheck) every line of code.


The Mars Climate Orbiter doesn't orbit

Back in physics class, our teachers leaped all over answers that consisted of a number. If the answer was 2.5, they'd take their red pens and write "2.5 what? Weeks? Puppies? Demerits?" And proceed to mark the answer wrong.

Back then, we thought that they were just being pedantic. But it's the kind of error that can burn up a $327.6 million project in minutes. It did in 1998, when the Mars Climate Orbiter built by NASA's Jet Propulsion Laboratory approached the Red Planet at the wrong angle. At this point, it could easily have been renamed the Mars Climate Bright Light in the Upper Atmosphere, and shortly afterward been renamed the Mars Climate Debris Drifting Through the Sky.

There were several problems with this spacecraft, its uneven payload made it torque during flight, and its project managers neglected some important details during several stages of the mission. But the biggest problem was that different parts of the engineering team were using different units of measurement. One group working on the thrusters measured in English units of pounds-force seconds, the others used metric Newton-seconds. And whoever checked the numbers didn't use the red pen like a pedantic high school teacher.

The result: The thrusters were 4.45 times more powerful than they should have been. If this goof had been spotted earlier, it could have been compensated for, but it wasn't, and the result of that inattention is now lost in space, possibly in pieces.