Some programs check for valid years by looking for the leading 1 or 19. The year 2000 ends in zeros. Some programs generate random numbers by dividing the system date by its last two digits. These programs can crash when they try to divide by 00. This might cause software that makes decisions based on the day of the week, for example, scheduling software, make the wrong decisions.
Problem is the biggest of problem of all.
We must suspect that every piece of hardware, every software package, every hand-built program and macro, every embedded system , and every data set will be affected. This includes software, programs, macros, and data on every size of computer, from the smallest personal computer to the largest host system . This 25-page Acrobat PDF article should not only convince you that you need to do something to prepare for the year 2000, it should give you a good idea what you should do, in particular what to look at and how to test. This is an important question. The program should require a century indicator on all dates that it receives and produces.