Aviation, banking, media and hospital systems were among the sectors hit by a bug in a software update that disrupted operations for many companies around the world on Friday.

Many of those using Microsoft Windows are likely experiencing a “blue screen of death” or error page. The problem is caused by a single bug in a software update from cybersecurity firm CrowdStrike, which provides antivirus software for Microsoft users.

The company released an update to the software overnight and at 1:30 a.m. EST, CrowdStrike reported that the software, called “Falcon Sensor,” was causing Microsoft Windows to crash and display a blue screen, Reuters reported.

George Kurtz, president and CEO of CrowdStrike, released a statement on X early Friday morning saying the incident was not a security issue or cyberattack. He added that the issue has been identified and the company has implemented a fix.

“We refer customers to the support portal for the latest updates and will continue to provide full and ongoing updates on our website,” Kurtz said.

The bug has caused major delays and cancellations at airports around the world. Flight-tracking data site FlightAware recorded nearly 24,000 delays and 2,300 cancellations worldwide as of 9:30 a.m. Friday. While some airlines have been able to get their digital systems back up and running, others are finding analog workarounds in the meantime.

The U.S. Department of Transportation said it was closely monitoring the situation and advised people facing delays and cancellations to use the website FlightRights.gov to help clear the delays to their travel.

In some states, 911 and non-emergency hotlines were unavailable, including Alaska, Virginia and New Jersey.

New Jersey Governor Phil Murphy released a statement early Friday morning indicating that the state had activated the State Emergency Operations Center in response to the disruptions and had issued guidance to other agencies on how to handle the situation.

“We are also engaging state and local governments, 911 call centers and utility companies to assess the impact and offer our assistance,” he said.

Microsoft published a troubleshooting guide for X early Friday morning.

By 10 a.m. on Friday, some global companies were seeing relief from their outages. Downdetector, which tracks outages in real time, showed that companies like Visa, Zoom, UPS and Southwest Airlines were returning to more normal operations than they had experienced in the early morning hours.

Speaking to the Today hosts this morning, Kurtz said he was “deeply sorry for the impact we’ve caused to customers, travellers and everyone who’s been affected.” He said some customers were able to restart and see progress in getting online, and that trend was likely to continue throughout the day.

The effects of Friday’s global IT outage were felt throughout the day, particularly at government systems and transportation hubs.

According to the Associated Press, courts in Massachusetts and New York experienced disruptions in service because court transcription systems in some Massachusetts courthouses were not operational.

The Texas Department of Public Safety, which operates the driver’s license offices, also closed its offices for the day. There is no estimate yet on when they will reopen.

Around 4:00 p.m. EST, Kurtz issued further statements about X, reiterating that the outage was not a security breach.

“We understand the seriousness of the situation and apologize for the inconvenience and disruption,” he said. “We are working with all affected customers to ensure systems are up and running again and that they can provide the services their customers rely on.”

Kurtz said the company is working on a “technical update and root cause analysis” that they will share with customers, and shared a letter that has been sent to customers and partners.

“We know that adversaries and malicious actors will attempt to exploit these types of events. I encourage everyone to remain vigilant and ensure you contact official CrowdStrike representatives. Our blog and technical support remain the official channels for the latest updates,” the message read.

“Nothing is more important to me than the trust our customers and partners have placed in CrowdStrike. As we resolve this incident, I am committed to providing full transparency into how this happened and the steps we are taking to prevent it from happening again,” it continued.