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.
I had always thought this is where the term "bug" came from, but the log says "First actual case of bug being found", which to me implies misperforming routines were called bugs prior to the "bug" being found.