An auto-correct fail is an error that occurs when the software created to detect and correct misspelled words replaces a user-generated mistake with a different, and possibly worse, error.
Auto-correct software identifies misspelled words, uses algorithms to identify the words most likely to have been intended, and edits the text accordingly. Most word processors and messaging platforms of various types include auto-correct as a feature.
Auto-correct programs work very well with common and straight-forward typos, such as "teh" for "the." However, when the error is less clear-cut, auto-correct programs can be unreliable. Usually, the errors are innocuous but there can be significant effects. In late April 2012, for example, two schools in Georgia were locked down after a student received the text message: "Gunman be at West Hall." The recipient (who was not the person the sender intended to contact) informed police immediately and security measures were put in place. The original message, however, was "gunna be at West Hall," sent to a friend to say where they could meet.
The incorrect replacement of misspelled words by auto-correct and spell-check programs is sometimes referred to as the Cupertino effect, a reference to the fact that Word ‘97 suggested Cupertino when "co-operation" was spelled without a hyphen. Cupertino is a small city in California, best known for being the home of Apple, whose iPhone auto-correct feature is notoriously error-prone.