Y 2k Problem

 Y2K means Year 2000.  31 dec 1999, after 12 o'clock Computer date would have becaome 1 jan 1900 not as 1 jan 2000. in this situation all the computer around the world would go back a century and many important task would stop.

Because until that time ( dec 31, 1999 ) the date format of  the computer was MM-DD-YY not as MM-DD-YYYY  .