Zero-defect software: The elusive goal: It is theoretically possible but difficult to achieve; logic and interface errors are most common, but errors in user intent may also occur

In October 1960, shortly after a new radar network to warn the United States of missile attacks had become operational, a radar station in Greenland reported the appearance of a massive attack - a large number of radar returns coming over the eastern horizon. The real cause of the alarm: the moon was rising.