Last Friday, 8.5 million computers around the world stopped working. All kinds of businesses were impacted, from airlines to banks to hospitals. The cause was a routine update sent out by a software company called CrowdStrike. WSJ’s Robert McMillan explains how the meltdown happened and why Microsoft’s software was especially vulnerable. Further Reading: - Blue Screens Everywhere Are Latest Tech Woe for Microsoft  - CrowdStrike Made Its Name Fighting Technology Problems. Now It Has Caused One.  Further Listening: - The Computer Glitch That Caused Nearly 1,000 Convictions  - Hacking the Hackers  Learn more about your ad choices. Visit megaphone.fm/adchoices