An apparent computer system outage is disrupting operations at airports, medical facilities and media outlets around the world.
The US Federal Aviation Administration said on Friday that American Airlines, United Airlines and Delta Airlines have grounded all their flights due to communication problems.
South Korea's Yonhap News Agency and other sources say some low-cost airlines in the country are facing problems with booking or issuing air tickets. Employees of some airlines are issuing tickets manually.
The apparent system failure is also affecting hospitals and emergency medical services.
Authorities in the US state of Alaska say the 911 emergency call service is not available due to a statewide technology-related outage.
Israel's health ministry says medical institutions in the country are affected. The ministry blames a software malfunction, not a cyberattack, as the cause of the trouble.
The impact can also be seen in TV stations and news agencies. British media network SkyNews had broadcasts interrupted temporarily by the outage.
George Kurtz, President and CEO of US cybersecurity firm CrowdStrike, said on social media that the company is working with customers impacted by a defect found in a single content update for Windows hosts.
Kurtz said Mac and Linux hosts are not impacted.
He also said this is not a security incident or cyberattack and that the issue has been identified, isolated and a fix has been deployed.