Flying Today? What You Need to Know About the Global Tech Outage.

Travel plans across the world were thrown into disarray on Friday, as a global technology outage disrupted businesses and services — including air travel — leaving thousands of flights canceled or delayed across the United States and beyond.

While service was slowly recovering by midmorning Eastern time, the ripple effect was still snarling travel plans as delayed and canceled flights created a buildup of passengers waiting at airports, and some planes and crews out of position.

“The anxiety is getting up a little,” said Adonis Ajayi, 35, at Ronald Reagan Washington National Airport on Friday morning. Mr. Ajayi was on his way to Key West, Fla., for a long weekend and said he had been checking social media constantly for flight updates — his flight had been delayed for nearly three hours. “I’ve never seen anything of this scale.”

The outage was caused by a flawed update from the cybersecurity firm CrowdStrike, whose software is used globally by scores of industries to protect Microsoft systems. Messages posted on social media by travelers worldwide showed flights grounded, some terminal monitors down and crowds of stranded passengers waiting at airport gates and customer service desks. Some passengers at one airport in India had to stand in long lines to obtain handwritten boarding passes.

Which airports have been hit the worst?

In the United States, Hartsfield-Jackson Atlanta International, the world’s busiest airport, appeared to have the most flights affected by the outage on Friday morning, with more than 230 incoming and outgoing flights canceled and more than 370 flights delayed, according to FlightAware, a real-time flight tracker.

Many other airports, including hubs in New York, Chicago and Charlotte, N.C., also appeared to experience significant disruption.