By Aditya Soni and David Shepardson
(Reuters) -AT&T said late on Thursday an outage that disrupted calls and text messages for thousands of U.S. users and prompted federal investigations was not caused by a cyberattack.
The carrier had restored wireless service for all affected customers, several hours after an outage that affected more than 70,000 users at its peak.
"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," the wireless carrier said in a statement on its website.
AT&T (NYSE:T), whose 5G network covers around 290 million people across the United States, has been grappling with interruptions to its service for more than 10 hours.
"We are taking steps to ensure our customers do not experience this again in the future," AT&T earlier said on its website.
The Federal Communications Commission said it was investigating the incident, while the U.S. Cybersecurity and Infrastructure Security Agency (CISA) said it was working with AT&T to understand the cause.
White House spokesman John Kirby (NYSE:KEX) said the FBI and the Department of Homeland Security (DHS) were looking into the AT&T outage. CISA is a unit of DHS.
"We are being told AT&T has no reason to think this was a cyber or security incident," said Kirby, adding that the FCC was in touch with the company.
"But the bottom line is we don't have all the answers," he said about the cause of the outage.
AT&T declined to comment on the FCC's investigation into the incident.
The company did not provide further details on the reason for the outage and the number of affected users.
AT&T shares were down 2.4% in afternoon trading. The number of outage incidents to about 3,255 by around 2:47 p.m. ET (1947 GMT), according to tracking website Downdetector.com.
The FBI also said that it was in touch with the company about the network outage. "Should we learn of any malicious activity, we will respond accordingly," it said in a statement.
Doug Madory, the director of internet analysis firm Kentik, said it was unclear from the outside what exactly had happened at AT&T, although he said he doubted it was the result of malicious activity.
"I'm skeptical this was some kind of an attack," he said in a telephone interview. "Most of these things end up being some kind of a software push that got screwed up somehow."
The outage affected people's ability to reach emergency services by dialing 911, according to posts on the X social media platform by government departments in several U.S. cities.
"We are aware of an issue impacting AT&T wireless customers from making and receiving any phone calls (including to 911), the San Francisco Fire Department said on X.
The Prince William County Police Department in Virginia and Charlotte-Mecklenburg Police Department in North Carolina posted similar statements on the platform.
Users of Verizon (NYSE:VZ), T-Mobile and UScellular also faced disruptions, but they were more limited than the AT&T reports, Downdetector showed.
The other companies said their network was operating normally and the outage was potentially related to customers trying to connect with other networks.
U.S. Senator Rick Scott of Florida said in a post on X that he had contacted AT&T for an update.
"Florida law enforcement is doing everything it can to keep people safe, and I expect AT&T to keep us informed on what it is doing to get 911 services fully back online ASAP," he said.
In 2021, regulators settled for $19.5 million a probe into a T-Mobile outage during the pandemic that lasted over 12 hours and led to more than 20,000 failed 911 emergency calls.