In software development, bugs in the code are inevitable. That\u2019s why companies push out software updates so often. But there is a specific kind of bug that is especially worrisome, something called a \u201czero day.\u201d It\u2019s a bug no one knows about \u2014 not even the software company \u2014 so it hasn\u2019t been patched and is vulnerable to hackers. Dina Temple-Raston, host of the podcast “Click Here,” has more on this story.