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First Instance of Actual Computer Bug Being Found was on September 9th, 1947 (Or was it?)
(education.nationalgeographic.org)
This is a most excellent place for technology news and articles.
I've seen people try to claim that this was actually the first computer bug, or worse the origin of the term, but that log entry very clearly establishes that the term was already in use in the modern sense of error/glitch and she was making the pun.