Always ready to pioneer new methods of problem-solving, Captain Grace M. Hopper made history on September 9, 1947, by removing the first computer bug. It was a moth that got into the relay calculator and was the first actual case of a bug being found.
Afterward, the operators coined the phrase that they have “debugged the computer.” Of course anyone with a computer science background probably knows that story.
At 3:45 p.m., Grace Murray Hopper records the first computer bug’ in the Harvard Mark II computer’s log book. The problem was traced to a moth stuck between relay contacts in the computer, which Hopper duly taped into the Mark II’s log book with the explanation: “First actual case of bug being found.” The bug was actually found by others but Hopper made the logbook entry.
Source: U.S. Navy Cryptology and Technology