First actual computer bug was found today, 66 years ago

Graham Cluley
Graham Cluley
@[email protected]

66 years ago today, on the 9th September, 1947, operators of the Mark II Aiken Relay Computer being tested at Harvard University, found something curious trapped between points at Relay #70, Panel F.

A moth.

First bug

A note made at the time explains, this was the “first actual case of bug being found”. History records that the legendary Grace Hopper was the person who located the moth, and in so doing, helped popularise the idea of “debugging computers”.

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Update: See the comments to this article below – which debunk Grace Hopper’s involvement in the discovery of the moth. Although it does appear she helped the incident gain exposure.

Grace HopperGrace Hopper, affectionately known as “Amazing Grace” and “Grandma COBOL”, went on to become something of a computing celebrity. A 20th Century Ada Lovelace, if you will.

Sadly, no record has been made of the moth’s identity for its considerable contribution to the world of technology, although it has achieved a certain immortality of its own thanks to a yellowing strip of Scotch tape.

The log book now resides at the National Museum of American History, but apparently is not currently on public view – which seems a shame.

Graham Cluley is an award-winning keynote speaker who has given presentations around the world about cybersecurity, hackers, and online privacy. A veteran of the computer security industry since the early 1990s, he wrote the first ever version of Dr Solomon's Anti-Virus Toolkit for Windows, makes regular media appearances, and is the co-host of the popular "Smashing Security" podcast. Follow him on Twitter, Mastodon, Threads, Bluesky, or drop him an email.

8 comments on “First actual computer bug was found today, 66 years ago”

  1. Wat

    Hopper did not find the moth, she just publicized it. This is not the first "bug" found in a electromechanical system, and the terms "bug" and "debug" predate the finding of this moth. The "First actual case of a bug being found" written in the log is a joke, because problems with systems had already been referred to as "bugs" well before this incident.

  2. This is not the first mention of bugs causing problems. Thomas Edison wrote in at least one letter about a bug in one of his inventions.

  3. Ben

    This version of the story is not correct, according to Smithsonian curator Peggy Kidwell. (The moth is currently interred at the Smithsonian.) The following is excerpted from the article "Smithsonian Honors the Original Bug in the System" (1997) by Peter Wayner.

    In recent years, credit for discovering the bug has gone to Grace Hopper, one of the Mark II's programmers at Harvard who went on to become a rear admiral in the U.S. Navy. However, Peggy Kidwell, the curator who designed the exhibit is setting the record straight.

    "There is a widely propagated myth that this is the first use of the term 'computer bug' and Grace Hopper was the one who discovered it," she said. "Neither of those myths, although they are both very appealing, are true." She points out that the note in the logbook was not made in Hopper's handwriting.

    Some of the confusion may have arisen because Hopper wrote and lectured widely on the topic. She was the author of several programming books that included the word in their glossaries. Kidwell also says that Hopper created a number of humorous illustrations of the different types of computer bugs infesting the Mark II computer. Hopper labeled a problem in some of the computational tables that were stored on tape as a "tape worm."

    Kidwell also points out that the word "bug" was already in fairly widespread use in technical circles in 1947. Thomas Edison used it to describe problems in his inventions. A 1934 edition of Webster's Second International dictionary also includes the meaning in the scope of the word.

  4. Selwynj Jackson

    On Digital Research's CP/M machines we used DDT (Dynamic Debugging Tool) to get rid of the bugs.

  5. The version I heard which makes the most sense to me is
    that Grace Hopper found (or was responsible for popularizing it)
    the first actual bug found in a computer. The use of the word bug
    in this sense was widespread before this, but that could be the
    first time someone actually and literally found a bug, in this case
    it was a moth.

  6. Ms H

    IEEE has a very nice article about Edison coining the term, "bug".

  7. Ms H

    "The Mark II Aiken Relay Calculator

    In the mid-1940s, Grace Murray Hopper was working on Harvard University's Mark II Aiken Relay Calculator. This primitive computer was based on relays, a type of electromechanical switch. On the September 9th of 1947, not 1945, the Mark II developed a malfunction. Operators, including William "Bill" Burke, investigated to find out what was wrong; contrary to many versions of the story, Grace Murray Hopper was not among them."

  8. Maxedwell

    I remember that as a winning, final question on “Who Wants to be a Millionaire”: What was the first bug found in a compute which gave rise to the popular expression: Bug in the system? Answer: moth

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