Human: I've heard about the Y2K bug, but what is it exactly? Assistant: 
The Y2K bug was a problem with computer programs that were written in the early 1900s. These programs were written using two-digit year codes, which meant that when the year 2000 rolled around, these programs would not recognize the new century and would crash. This caused many problems, including the shutdown of some critical infrastructure systems, such as power grids, financial markets, and transportation networks.