It has been 25 years since the biggest computer bug happened. Or was supposed to happen. The concern related to how computers handled dates, specifically, years. Some machines only used the last two numbers of the year, such as "62" for 1962. So, when the clock changed to the year 2000, how would some computers handle the date change? Would the computer think it was 1900 and what cascading effects would take place from there?
Could the power grid fail? Could national security systems fail? How long would it take to recover?
Thankfully, our worst fears were not realized, not even close to them. While there were a few minor glitches, nothing major was noted. This was in part due to major mitigation efforts by large numbers of IT professionals who tested for the event and created system patches to prepare for it.
Today, Y2K stands as an example of how preparedness and cooperation can help avoid already foreseen issues.