Everything from airlines to banks to retailers were impacted in many countries.

Across the world, critical businesses and services including airlines, hospitals, train networks and TV stations, are being disrupted by a global tech outage affecting Microsoft users.

In many countries, flights have been grounded, workers couldn’t access their systems and, in some cases, customers haven’t been able to make card payments in stores.

A series outages rippled across the globe as information displays, login systems and broadcasting networks went dark.

The problem affecting the majority of services was caused by a flawed update by CrowdStrike, an American cybersecurity firm, whose systems are designed to protect users from hackers. Microsoft said on Friday that it was aware of an issue affecting machines running “CrowdStrike Falcon.”

But Microsoft had also said there was an earlier outage affecting Azure users, its cloud service system, in the United States. Some users may have been affected by both.

It’s more apt to ask what wasn’t affected. Everything from airlines to banks to retailers were impacted in many countries.

In Australia, passengers were stuck in long lines at Sydney airport as information screens went blank, and programming was disrupted at the national broadcaster. Airports in Europe and Asia, including in Britain, Germany and Taiwan, had long delays at check-ins and flights were delayed or canceled. At an airport in South Korea, handwritten boarding passes were being slowly handed out.

A few hospitals in Germany said they would cancel elective procedures; and in Britain, some doctors in the National Health Service weren’t able to access systems. Sky News, a major news channel in Britain, couldn’t operate, while customers at some Waitrose supermarkets couldn’t make card payments.

People at Disneyland Paris theme park were also affected, as screens displaying wait times for rides went down.

But the problems weren’t uniform. London’s Heathrow Airport said that its flights were still operating. The London Stock Exchange said that it couldn’t publish news updates but the exchange, where trades take place, was working as normal.

In some cases, issues were resolved relatively quickly. In Ukraine, Sense Bank and the mobile operator Vodafone reported brief problems accessing their services. At Dubai International Airport, two airlines switched to alternative systems, allowing operations to resume. At about 5 a.m. E.T., American Airlines said it had re-established its operations.

George Kurtz, the president and chief executive of CrowdStrike, said the company “is actively working with customers impacted by a defect found in a single content update for Windows hosts.” In a post on X, Mr. Kurtz added that Mac and Linux hosts are not affected.

“This is not a security incident or cyberattack,” he added. “The issue has been identified, isolated and a fix has been deployed.”

After a few hours, some services were coming back online. Microsoft also provided suggestions to users to help resolve the issue, including restoring backup systems, on a services page that tracks issues with Azure.