CrowdStrike outage: What we know 4 days after a software update brought down computer

CNN
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Hundreds of US flights were canceled early Monday, as airlines work to recover four days after a global tech outage caused massive delays and left travelers stranded at airports around the nation.

More than 700 flights into, within or out of the United States were canceled by 7:30 a.m. ET Monday, and more than 800 flights were delayed, according to flight tracking site FlightAware.

While most airlines have brought their cancellation numbers down, more than 600 of Monday’s canceled flights were from Delta Air Lines, according to FlightAware.

Delta declined to comment on the numbers, but in an update to customers Sunday afternoon, Delta Air Lines CEO Ed Bastian said the company is working to restore operations after the outage.

The “largest IT outage in history” – prompted by a software update for Microsoft devices late Thursday into the early hours of Friday – brought down computers and technical systems across the world, causing disorder at airports, outages for 911 services and challenges at health care facilities.

“In particular one of our crew tracking-related tools was affected and unable to effectively process the unprecedented number of changes triggered by the system shutdown,” Bastian said in the statement.

The outage affected an estimated 8.5 million Windows devices – less than one percent of all Windows machines, according to a Saturday blog post from Microsoft. But the effects were ubiquitous, with airlines, banks, businesses, schools and governments, along with some health and emergency services, across the world affected.

Costs from the outage could top $1 billion, Patrick Anderson, CEO of Anderson Economic Group, told CNN. But it’s unclear if – and how – any customers affected will be compensated.

Here’s what we know about the outage and its continued effects.

The outage was related to a software update rolled out by CrowdStrike, a major US cybersecurity firm. The software – used by numerous Fortune 500 companies, including major global banks, health care and energy companies, as well as by the US government –detects and blocks hacking threats.

CrowdStrike told customers early Friday the outages were caused by “a defect found in a single content update of its software on Microsoft Windows operating systems,” according to a post on X from CEO George Kurtz. The issue was identified and isolated, and engineers deployed an update to fix the problem, Kurtz said.

The company’s engineers took action to address the problem, according to an advisory viewed by CNN, which told customers to reboot their computers and perform other actions if they were still having technical issues. The issue is specific to Falcon, one of CrowdStrike’s main software products, and is not impacting Mac or Linux operating systems, according to the advisory. Crowdstrike says Falcon is designed to protect files saved in the cloud.

The company said the outage was not caused by a security incident or a cyberattack.

Kurtz later apologized to customers and said the company is “deeply sorry for the inconvenience and disruption.”

In an update posted to LinkedIn late Sunday, CrowdStrike said “a significant number” of the 8.5 million devices were back online and operational.

Chaos and confusion for travelers

On Sunday, more than 1,800 US flights were canceled and more than 9,900 delayed, according to FlightAware. Major hotels, including Marriott International and some Hiltons, were impacted both in regard to payment processing and delays to check in-processes.

US-based carriers American Airlines, United Airlines, Delta Air Lines, Allegiant Airlines, SunCountry and Frontier Airlines all reported issues on Friday.

American Airlines said Friday morning it was able to “safely re-establish” operations. By Friday night, United said “most of our systems have recovered,” but cautioned there may still be some flight delays or cancellations as a result of the issues.

Delta Airlines paused all its flights Friday morning while its systems were offline, and more than 3,500…