Many media outlets are currently reporting that a "computer error" or "computer glitch" enabled thousands of United Airlines customers to purchase transatlantic first class flights for a fraction of their normal price as long as they paid with Danish Kroner.
What was behind the error? Someone entered the wrong pound-to-kroner exchange rate and then, presumably, failed to double-check the entry and have the entry checked and signed-off by a peer.
This was NOT a computer error. If the media did a better job of reporting these kinds of errors for what really are i.e. human errors and, in this case, a data entry error compounded by a quality control problem, then maybe more enterprises would put proper safeguards in place to ensure that they don't happen.
Source: Wikimedia Commons