Industries ranging from healthcare to banking, air travel, and others were hit by a global IT outage on Friday, July 19th, that impacted 8.5 million Windows PCs and servers connected to the CrowdStrike security platform.

CrowdStrike’s faulty update took down these machines, but the company has fixed the issue and has been working with businesses to get them back online. Microsoft has also released a bootable USB drive tool that can help restore crashed systems.

CrowdStrike, which is a cybersecurity firm based in the US, has explained that a flawed sensor configuration update was the culprit. The company blames a bug in test software for not properly validating the content update that was pushed out to millions of machines on Friday. CrowdStrike is promising to more thoroughly test its content updates, improve its error handling, and implement a staggered deployment.

Banks, airlines, TV broadcasters, supermarkets, and even Starbucks had systems crashed due to the problem, and on Monday, Delta Airlines canceled over 600 flights while it continued to deal with the issue.

Read on below for all of the details about this massive global problem and what is being done to fix it.