One of the top cyber security firms has blamed a faulty system update as the cause of a Friday morning technology outage that has caused major disruptions with the operations of major airlines, media companies, banks, medical facilities and telecoms firms around the globe.

Crowdstrike, a U.S. firm that advertises being used by over half of Fortune 500 companies, said one of its recent content updates had a defect that impacted Microsoft’s Windows Operating System, adding that the incident was “not a security incident or cyber attack.”

“The issue has been identified, isolated and a fix has been deployed,” said a statement from Crowdstrike. Microsoft, meanwhile, said “the underlying cause has been fixed,” but that residual impacts continue to affect some of its Microsoft 365 apps and services.

In the U.S., hundreds of flights were canceled Friday morning. American Airlines, Delta Airlines and United Airlines were among those who grounded flights less than an hour after Microsoft said it resolved a cloud-services-related outage that impacted several low-cost carriers. The FAA recommends that if you are scheduled to fly out today, to reach out to your airline to confirm the status of your flight.

Public transit systems in the U.S. reported impacts. The Washington Metropolitan Area Transit Authority in Washington D.C. said its “website and some of our internal systems are currently down,” but that trains and buses were running as scheduled. In New York City, the Metropolitan Transportation Authority also said it’s buses and trains were unaffected but that “some MTA customer information systems are temporarily offline due to a worldwide technical outage.”