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5 things to know about the massive AT&T network outage

By Brian Fung, Catherine Thorbecke and Clare Duffy, CNN

(CNN) — Tens of thousands of Americans had trouble making phone calls, sending texts, reaching emergency services or even accessing the internet on Thursday because of a nearly 12-hour AT&T network outage.

And at least one police department reported that its 911 line was briefly flooded with people dialing to see if their calls would go through from their cell phones.

The alarm over an outage of a major cell network that at one point affected more than 70,000 customers is understandable.

People have become deeply reliant on their cell phones for keeping in touch with work and family, getting directions, accessing the internet and doing two-factor authentication for website logins — not to mention more serious tasks like calling for help when in danger.

The incident also quickly raised questions about whether malicious activity could have caused the outage and could present an ongoing threat to US cell networks, although there is currently no evidence that bad actors were behind the outage.

AT&T finally restored wireless service to all customers by around 3 pm ET, and the company said it was “sincerely” sorry to customers.

Here’s what you need to know about the outage:

Who was affected?

If you’re a Verizon or T-Mobile customer and don’t have friends or family who use AT&T, you may not have noticed the issue on Thursday, as those rival carriers were not affected.

But starting early Thursday morning, thousands of AT&T customers began reporting issues calling, texting and accessing the internet on their mobile devices. At one point, more than 74,000 AT&T customers reported outages on digital-service tracking site DownDetector. The figure only represents self-reported outages, meaning the true number of affected customers was almost certainly higher.

Prior to Thursday’s incident, AT&T had encountered sporadic outages this week, including a temporary 911 outage in some parts of the southeastern United States. Although regional outages happen occasionally, prolonged nationwide outages are exceedingly rare.

Within hours on Thursday, the number of customers affected by the outage began to decline. And by around 3 pm ET, the company said the issue had been fully resolved.

Several local governments said on Thursday that the AT&T outage was causing disruptions and that in some cases AT&T customers were unable to call emergency services and would have to instead do so with a landline or a cell phone from a rival carrier. New York Police Department officials told CNN that they were not able to make calls or utilize emails on AT&T phones Thursday morning unless they were connected to Wi-Fi.

However, an AT&T spokesman said the company’s FirstNet network remained operational despite the outage. FirstNet provides coverage for first responders, including police and fire departments, and is advertised as a more robust network than the AT&T commercial network. It uses a mix of its own infrastructure plus AT&T’s broader network.

What caused the outage?

AT&T posted an update on Thursday evening, saying that the company does not believe the outage was due to a cyberattack.

“Based on our initial review, we believe that today’s outage was caused by the application and execution of an incorrect process used as we were expanding our network, not a cyber attack. We are continuing our assessment of today’s outage to ensure we keep delivering the service that our customers deserve,” the company posted.

What did government officials have to say about the incident?

Various federal agencies are investigating the incident. That includes the Federal Communications Commission, the Federal Bureau of Investigation and the Department of Homeland Security.

“We are aware of the reported wireless outages, and our Public Safety and Homeland Security Bureau is actively investigating,” the FCC said in a statement Thursday afternoon on X. “We are in touch with AT&T and public safety authorities, including FirstNet, as well as other providers.”

The FBI, meanwhile, said in a statement to CNN that it is in contact with AT&T regarding the outage. “Should we learn of any malicious activity we will respond accordingly,” the FBI statement added.

The White House also responded on Thursday, saying that federal agencies are in touch with AT&T about network outages but that it doesn’t have all the answers yet on what led to the interruptions.

White House National Security spokesman John Kirby said that work was ongoing. “The bottom line is we don’t have all the answers to that,” Kirby said Thursday afternoon. “And so we’re working very hard to see if we can get to the ground truth of exactly what happened.”

How did AT&T respond?

AT&T said it took “immediate action” to restore about three-quarters of the network by around lunch Eastern time. Then, about 12 hours after the outages first began, AT&T announced it had fully restored service to affected customers.

“We sincerely apologize to them (customers),” the company said in a statement. “Keeping our customers connected remains our top priority, and we are taking steps to ensure our customers do not experience this again in the future.”

Telecom industry analysts say that AT&T could potentially face fines over the 911 outages, although that isn’t a certainty.

Many angry customers, meanwhile, flooded AT&T with inquiries on social media and blasted the company’s apparent lack of transparency around what was going on and when service would be restored. On X, AT&T’s official customer service account urged customers to send the company direct messages.

AT&T’s share price ended the day down more than 2% on Thursday following the outage, the same day that the S&P 500 and Dow Jones Industrial Average hit record highs.

What does this say about the security of US cell networks?

At this point, federal authorities and an industry official say there’s no evidence of a cyberattack. The industry official told CNN the problem appears to be related to peering, or the way that calls are handed off from one network to the next.

It’s possible new evidence could emerge pointing to an attack. But it is too soon to say.

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