Y2K was a notable computer bug resulting from the practice in early computer program design of representing the year with two digits. This time code ambiguity caused some date-related processing to operate incorrectly for dates and times on and after January 1, 2000 and on other critical dates which were billed "event horizons". Without corrective action, long-working systems would break down when the "...97, 98, 99..." ascending numbering assumption suddenly became invalid. Companies and organizations world-wide checked, fixed, and upgraded their computer systems.
While no globally significant computer failures occurred when the clocks rolled over into 2000, preparation for the Y2K bug had a significant effect on the computer industry. Countries that spent very little on tackling the Y2K bug (including Italy and South Korea) experienced as few problems as those that spent much more (such as the United Kingdom and the United States), causing some to question whether the absence of computer failures was the result of the preparation undertaken or whether the significance of the problem had been overstated.