The Millennium bug
The Year 2000 problem is also known as the Y2K problem, the Millennium bug, the Y2K bug, or Y2K. Problems arose because programmers represented the four-digit year with only the final two digits. This made the year 2000 indistinguishable from 1900. The assumption that a twentieth-century date was always understood caused various errors, such as the incorrect display of dates, and the inaccurate ordering of automated dated records or real-time events.
In 1997, the British Standards Institute (BSI) developed a standard, DISC PD2000-1, which defines “Year 2000 Conformity requirements” as four rules:
1) No valid date will cause any interruption in operations.
2) Calculation of durations between, or the sequence of, pairs of dates will be correct whether any dates are in different centuries.
3) In all interfaces and in all storage, the century must be unambiguous, either specified or calculable by an algorithm.
4) Year 2000 must be recognized as a leap year.