The Year 2000 problem ( also known as the Y2K problem , the millennium bug , Y2K Bug , and Y2K ) was a problem that happened because of the way in which some early computer programs were designed . The Year 2000 problem ( also known as the Y2K problem , the millennium bug , the Y2K bug , or simply Y2K ) was a problem for both digital ( computer-related ) and non-digital documentation and data storage situations which resulted from the practice of abbreviating a four-digit year to two digits .