Even as computers became cheaper, programmers for years still used two-digit years. Computers will think it's 1900. They'll either churn out nonsense or fry their circuits. Seems like it should be simple to fix, and it is - once you find all the places where you have to fix it. One analogy is that it's like knowing that you have to fix a rivet on the Golden Gate Bridge, but first you have to find which rivet is broken.
Software can have millions of lines of code.
Software from one computer interacts with other computers in a company or across networks, so all computers have to be fixed or the 00s will spread again like a virus. There is no quick way to fix the bug and none are likely to come around, experts say. Software specialists have to get in and crawl through every bit of code. And if it's not fixed, lots of bad things could indeed happen. If the bug brings down a plant, the nation's power grid will try to compensate for the power shortage, potentially causing regional blackouts.