How did the phrase A bug in the computer get started?

This question has spawned a number of urban myths.

The term 'bug' was first used by Grace Hopper on September 9th, 1945 when a real bug, a moth, short-circuited an early computer on relay number 70 Panel F, of the MARK II Aiken Relay Calculator, in the Harvard University. The operators of the computer said they had "debugged" the computer, and ever since then the terms has not changed. (They actually finished building the computer in 1947, which was the year of the actual event.)

The most widely known is that Captain (later Admiral) Grace Hopper was busy debugging a program that she had written. Finding a moth squashed in her card deck, she quipped "this is the first real computer bug !"

This story gives the lie to the claim that this is where the name came from. If this was the first computer bug, why did she refer to it as the first real one ?

Come to that, why was she debugging her program before the moth was found?

The simple truth is that difficult to find troubles in machinery were already being called bugs by engineers prior to 1900. Tomas Edison may have been the first one to use the term in this sense, writing it in a notebook entry in 1876 regarding problems developing a system of multiplexing signals over a wire for telegraph.