Y2K problem
n. A computer bug that, if not fixed, will cause computers and devices with embedded microchips to fail or produce erroneous results beginning on January 1, 2000. (Also known as the millennium bug.)

Example Citation:
"Already struggling to wean hundreds of its schools from 19th-century-style coal furnaces before the dawn of the 21st century, the New York City Board of Education has received another premillennial warning, this one from the State Comptroller: the board is not moving fast enough to inoculate school computers against the so-called Y2K problem."
—Jacques Steinberg, "State Wants School Board To Move Fast on Y2K Problem," The New York Times

It's estimated that to fix the Y2K problem will cost businesses about US$600 billion over the next few years. Why all the fuss over what appears to be a simple date change? Many older software programs — especially mainframe-based applications used in banking, insurance, and government — store dates using two-digit numbers for the day, month, and year (e.g., MMDDYY). That's fine for the day and month, but a two-digit year means that 1999 is stored as 99 and 2000 is stored as 00. So January 1, 2000 will appear to the computer as January 1, 1900, and suddenly you'll be *very* late with your mortgage or loan payments! Fixing this problem requires hiring large teams of programmers to comb every one of the sometimes millions of lines of code in these legacy systems to discover where dates are used, and then to rewrite the code and restructure the underlying databases to handle four-digit years.

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