BUG INFORMATION SHEET The term "bug" is now universally accepted by computer users as meaning an error or flaw -- either in the machine itself or, perhaps more commonly, in a program (hence the phrase "debugging a program").	The first official record of the use of the word "bug" in the context of computing is associated with a relay-based Harvard Mark II computer, which was in service at the Naval Weapons Center in Dahlgren, Virginia. On September 9th, 1945, a moth flew into one of the relays and jammed it. The offending moth was taped into the log book alongside the official report, which stated: "First actual case of a bug being found."
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It has now become a popular tradition that it was the legendary American Naval officer and mathematician Grace Murray Hopper who found the offending insect, but it's also said that she wasn't there when it happened. (Grace was a pioneer in data processing and is credited with developing the first compiler, which is a program that translates a high-level human-readable language into the machine language understood by the computer. In 1983, Grace became the first woman to achieve the rank of rear admiral in the United States Navy.)
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It is also widely believed that this incident was the origin of the term "bug" itself, but this is also not the case. If you read the wording of the report carefully, you can see that the writer is really saying: "Hey, we actually found a bug that was a real bug!"

In fact the word "bug" was already being used in Thomas Edison's time to imply a glitch, error, or defect in a mechanical system or an industrial process. Furthermore, "bug" was used as far back as Shakespearean times meaning a frightful object.