Top 15 Worst Computer Software Blunders

“There is no reason for any individual to have a computer in his home.” This quote, famously muttered by Ken Olsen, founder and CEO of Digital Equipment Corporation, today makes for an interesting bit of comic relief in the history of personal computing.

But if the performance of our home computers were anything like what you’re about to read, we’d be inclined to agree. These Top 15 Worst Computer Software Blunders led to embarrassment, massive financial losses, and even death.

Needless to say, computers and the software that makes them useful, have an even larger impact on our lives than Olsen could have expected, and when things go wrong, they really go wrong.

1. St. Mary’s Mercy Medical Center Kills Its Patients, On Paper

In February 2003, Baseline reported on a computer software blunder at St. Mary’s Mercy Medical Center in Grand Rapids, Michigan, that cost the lives of 8,500 patients. Well, not really. In actuality, each of the patients, who had procedures done from October 25 through December 11 of the previous year, were alive and kicking. However, the glitch, attributed to the hospital’s patient management system, notified Social Security, patient insurance companies, and the patients themselves, of the “unfortunate” demises. St. Mary’s spokeswoman Jennifer Cammenga had this to say: “To us, this is really not a very big story. We’re not going to elaborate any more … It was a mapping error. That’s all we have to say about it.”

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2. Knight Capital Group Loses Nine Figures in 30 Minutes

Knight Capital Group, a market-making firm that until August 2012 had a stellar reputation in its industry, blew all of that in about 30 minutes. Between 9:30 a.m. and 10 a.m. EST on August 1, the company’s trading algorithms got a little buggy and decided to buy high and sell low on 150 different stocks. By the time the bleeding had stopped, KCG had lost $440 million on trades. By comparison, its market cap is just $296 million and the loss was four times its 2011 net income. Furthermore, the company’s stock price dropped 62 percent in one day, according to Bloomberg Businessweek.

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3. World War III Narrowly Averted

Russia — or Soviet Air Defence officer Stanislav Petrov, to be exact — may have saved the world on the night of September 26, 1983, when the Soviet nuclear early warning system malfunctioned and erroneously reported that the US had launched an attack on his country. Petrov later told the Washington Post that he “had a funny feeling in my gut” that the alarm was false, which was confirmed through further investigation.

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4. Intel Pentium Stinks at Long Division, and Customer Service

In November 1994, the New York Times reported on a rather embarrassing issue with Intel Pentium chips that had affected a variety of PCs. A number of chips were flawed in a way that prevented them from accurately handling long division — unnoticeable to the common PC owner but a big deal for scientists and engineers, who required precise calculations in the handling of their work. Intel refused to recall the chips, stating that it wouldn’t affect that many people. For those who needed the precision, they were forced to “prove” why it mattered to them. There is nothing better than giving your customers a flawed product and then putting the burden of proof on them before deciding to make reparations. That’s customer service par excellence.

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5. AT&T Demonstrates How Not to Upgrade Software

On January 15, 1990, AT&T customers were hit with an outage that resulted in about nine hours of downtime in which no one could make long distance calls. According to PhWorld, the outage happened when a “software glitch managed to disable many switches throughout the network.” The company had just undergone a new software installation, which created the problem. Once the fault was found in the newer version, the company was able to install a previous version and get millions of angry customers back on the line.

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6. World Of Warcraft Creates Literal Computer Virus

On September 13, 2005, there were a whole lot of peeved geeks when new creation Hakkar, the god of Blood, hit the World of Warcraft and took the whole “computer virus” thing literally. Hakkar hit players with a “Corrupted-Blood” virus that had the ability to instantly kill off weaker characters. The virus was supposed to be contained to Hakkar’s kingdom, according to a report from the BBC, but through a programming glitch, it was passed on to other parts of the kingdom resulting in a 1,000+ “death” toll. Blizzard Entertainment, the game’s creator, eventually incorporated some quick fixes along with rolling restarts to negate the Hakkar effect.

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7. Apple Maps Goes Nowhere Fast

With the 2012 Apple iOS 6 update, the company decided to kick the superior Google Maps platform to the curb in favor of its own system. Unfortunately, it did a poor job of mapping out locations resulting in one of the most epic fails of the mobile computing movement. TPMIdeaLab noted the software was “missing entries for entire towns, incorrectly placed locations, incorrect locations given for simple queries, satellite imagery obscured by clouds and more” in a September 2012 report. David Pogue of the New York Times added that it was the most embarrassing, “least usable piece of software Apple has ever unleashed.”

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8. Michigan Dept. of Corrections Grants Prisoners Early Release

In October 2005, The Register reported on the early release of 23 prisoners due to a computer programming glitch with the Michigan Department of Corrections. The accidental early release dates came around 39 to 161 days early while an undisclosed number of inmates were kept in jail past their release dates. State assembly representative Rick Jones was concerned about the matter, but noted that he was “glad it’s not murderers.” However, that’s more than could be said for the next entry on our list of worst computer software blunders.

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9. California ‘Paroles’ 450 Violent Offenders (Without Supervision)

We suppose the Michigan Department of Corrections computer software blunder can be forgiven since all of the 23 offenders released were non-violent. While embarrassing, at least it wasn’t as insane as California’s release of 450 high-risk, violent prisoners, who were unleashed on an unsuspecting public in 2011, CBS News reports. The state was tasked with reducing its prison population by 33,000 with an obvious preference toward non-violent offenders. But due to a mistake in its computer programming, California gave “non-revocable” preference to approximately 450 violent felons, who due to the classification, did not have to report to a parole officer. At last report, many of the felons remain free.

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10. IRS Costs America Close To $300 Million

The Internal Revenue Service has never been an organization to turn down money, except in one now-famous instance in 2006 where it trusted a computer program to call out potential fraud cases in returns claiming refunds. The tax collection agency wasn’t aware their program was inoperative until it was too late, costing what the Associated Press via the Houston Chronicle estimates was between $200 million and $300 million in revenue. But that’s okay. We’re sure they’ll handle the Affordable Care Act without a hitch.

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11. Mars Climate Orbiter: The $327 Million Disaster

The Mars Climate Orbiter launched on December 11, 1998, with the intention of bringing the United States unprecedented understanding of the only other planet in the solar system deemed capable of supporting life. Unfortunately, due to an error in the ground-based computer software, the $327.6 million project — according to the NASA fact sheet — went missing 286 days later. Because of a miscalculation, Orbiter entered the Mars atmosphere at the wrong entry point and disintegrated shortly thereafter. D’oh!

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12. Race Condition Bug Creates Blackout for 50 Million

On August 14, 2003, a blackout across eight US states and Canada affected 50 million people. PC Authority described the cause, a race condition bug, as something that occurs when “two separate threads of a single operation use the same element of code.” Without proper synchronization, the threads tangle and crash a system. That’s what happened here with the result 256 power plants offline. The major disruptions manifested themselves in the form of cellular communication with the best form of communication during the outage said to be a laptop using a dial-up modem. And if you just cringed in horror at the word “dial-up,” you’re not alone.

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13. Microsoft Accuses Paying Customers of Piracy

If you thought Xbox One was the first example of Microsoft trying to sell you something while continuing to claim ownership over what you’ve just purchased, then you’ve forgotten about the “Get Genuine” debacle of 2006. The Microsoft Windows Genuine Advantage tool was designed as anti-piracy tech that would verify a Windows version as legitimate. But in 2006, it became more well-known as a buggy PR nightmare in which the company inadvertently accused paying customers of pirating legitimately purchased software. According to TechDirt’s Mike Masnick, there were more than 1,000 cases in which users were locked out of their software’s features. Masnick summed this one up best: “treating all your customers as criminals tends not to be a great business strategy.”

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14. EDS Child Support System Is Anything But

Since 2004, Electronic Data Systems (EDS) has been maligned throughout much of the U.K. for a massively unpopular software program it built for the Child Support Agency. Complaints are registered frequently, such as this one detailed by The Register in 2010. A recap given by Sun Dog Interactive in 2009 revealed that over a five-year span, there were 1.9 million people who had overpaid into the system, 700,000 who had underpaid, and around $7 billion in uncollected child support payments along with a backlog of 239,000 cases and 36,000 new cases “stuck” in the system. As you can see from the image, it’s a problem so rampant there is even a website devoted to the agency’s screw-ups, fittingly titled

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15. Patriot Missile System Timing Issue Leads To 28 Dead

By far the most tragic computer software blunder on our list occurred on February 25, 1991, during the Gulf War. While the Patriot Missile System was largely successful throughout the conflict, it failed to track and intercept a Scud missile that would strike an American barracks. The software had a delay and was not tracking the missile launch in real time, thus giving Iraq’s missile the opportunity to break through and explode before anything could be done to stop it, according to the US Government Accountability Office. In all, 28 were killed with an additional 100+ injured.

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Those were our picks for the Top 15 Worst Computer Software Blunders. Which ones did we leave off the list? Share your thoughts in the comments section.

  • kfitch42

    Seriously, how could you leave off the Therac 25? Its taught in just about every software engineering course.

    • Tom Faltesek

      Wow! That’s terrible. Perhaps a 16th entry is in order.

    • Marc W.

      Yeah, that case is in computer science curriculums

  • mario
  • This is a nice list. The Therac 25 example is definitely “mind blowing” and that should have made the list. But overall, this has some pretty solid entries. Definitely worth a read!

  • Frinkk

    “4. Intel Pentium Stinks at Long Division, and Customer Service”

    Pentiums don’t do “long division”, and I’m not even sure how that algorithm could be adapted to floating-point numbers. CPUs use completely different division algorithms.

    Second, the problem was not the bug, but the PR hit. I can’t think of a single CPU ever made that doesn’t have some bug or other. (Even the simple and venerable 6502 had bugs.) The issue with the Pentium division bug is that it was easily seen by users, and was happening right when PCs were becoming household appliances, rather than scientific or hobbyist instruments. Hobbyists know that CPUs have bugs. Everyday consumers, it turns out, did not.

    You can’t exactly fault Intel for their response, either. Almost nobody was actually affected by the bug. Do *you* want to manage a recall of the #1 desktop CPU in the world?

    In terms of actual problems, the Intel Pentium “F00F” bug was far more severe.

  • Daisy

    I realize this is a “worst offenders” list, but on a less tragic list you can’t forget a few years ago when all of us who rely on iPhone alarms to get up in the morning were an hour late heading to work. The alarm functionality just didn’t update to–was it a daylight savings time change or a new year? I don’t remember, and all the links I seem to find online reference what happened in the UK rather than here in the states, where I could apparently could have been prepared issue if I had been reading the news of what had already happened in Europe. I had to delete my alarms and recreate them for the feature to work correctly again. You’d think programmers with a company as big and powerful as Apple would be able to if/than/else themselves away from such disasters!

  • bob bray

    long time ago i worked on a system called FUNAC it had a mouse but was not VGA. think about that. also it controlled machines bigger than a car at very high speeds.

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  • Kelly

    Great list, though I really think #1 has to be the biggest blunder. The thought of knowing your family member has died must be a horrible feeling. It’s also a tossup between that and #15. I mean actually killing people due to a timing issue is really screwed up. I wonder how many lawsuits were issued….

  • Maggie

    Interesting list, I didn’t even know most of these blunders happened. I also didn’t know that a simple code bug is what caused the blackout. I remember it being worse for those who experienced the blackout when living in big cities. I think it gave a good sign of whats to come when a major apocalyptic even occurs.

  • April S.

    Excellent list you’ve got here. It’s a shame the effect that technology has on our society. A simple mistake can either kill people, ruin lives, create confusion, or back out a whole region of the USA!

  • Marcus L

    The black out had to have been the worst of it. It set a precedence as
    to what will happen when the world goes to crap because we have relied
    on technology too much. I for one am trying to become a little less
    dependent on technology by making a few changes in my life. And the
    smartphone (iphone) blunder is another great example.

  • JimL

    For item #15, we forgot how many of the patriot missiles worked as intended and focused on the one that didn’t. Before the incident cited, the Saudi’s were able to ignore the air raid sirens and continue with their lives. Just goes to show that life isn’t 100% perfect.

  • AshuA

    I saw this on some Nova program or another such list of space disasters. It was about a ‘laser’ to be stationed in space by Russia. The massive vehicle cleared the launch site and well on its way. The payload was attached inverted to the main rocket. And after main rocket separation it was designed to rotate 180 degrees and fire to continue to its destination… but the software error caused it to rotate 360 degree, and causing it to reenter and burn up ! Someone may know the details … feel free to attach the wiki link or details.

  • Thanks for these great examples of the impact of poor quality!

  • AS

    Many years ago, some of my fellow employees went to a client’s site to demonstrate or install the company’s software. Right in front of the customer, as they attempted to run the business software, a game that wasn’t supposed to be there unexpectedly came up!

  • jhnson

    Its an nice posts regards worst computer software blunders i agree with some times our advanced technology let us failure due to minor technical problems or some times it causes major probelm


  • david hays

    Wasn’t #11 because of someone not recognizing that parts of the system was in inches and part in the metric system?

    • Tom Salonek


      Yes, the infamous “metric mix-up” as noted in failure on Wikipedia “Specifically, the flight system software on the Mars Climate Orbiter was written to take thrust instructions using the metric unit newtons (N), while the software on the ground that generated those instructions used the Imperial measure pound-force (lbf). This error has since been known as the “metric mixup” and has been carefully avoided in all missions since by NASA.[16]”

  • Patrica Lauren

    This week’s list of worst software disasters should be more controversial, Since then a group of fantastics have kept the programe alive. Here are the list of top 10 Freeware Programes.

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  • Really, More comprehensive and i appreciate your blog.Thanks for post.


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