AT&T said the network disruption that caused tens of thousands of customers to lose cellular service Thursday was not the result of a cyberattack.
After service was fully restored at around 6 p.m. ET, the mobile phone service provider revealed the results of its initial investigation into the outage.
"Based on our initial review, we believe the outage was caused by the application & execution of an incorrect process used as we were expanding our network, not a cyberattack," AT&T posted on X.
"We are continuing our assessment to ensure we keep delivering the service that our customers deserve," the company said.
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AT&T's service suffered a national outage on Thursday, beginning at about 3:30 a.m. ET, according to Downdetector. Just before 2 p.m. ET, the number of reports had declined drastically to nearly 4,900 after spiking to more than 73,000 just after 9 a.m. ET.
Downdetector, a website that tracks phone and internet service outages, reported AT&T service was down mostly in the Atlanta, Chicago, Houston and Miami service areas.
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"Some of our customers are experiencing wireless service interruptions this morning. Our network teams took immediate action and so far three-quarters of our network has been restored. We are working as quickly as possible to restore service to remaining customers," AT&T said in a statement to FOX Business.
A U.S. defense official told Fox News there was "no indication it was a cyber attack."
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The FBI and Federal Communications Commission (FCC) said they were aware of the outages and investigating.
"We are aware of the reported wireless outages, and our Public Safety and Homeland Security Bureau is actively investigating," the FCC posted on X. "We are in touch with AT&T and public safety authorities, including FirstNet, as well as other providers."
The FBI also said it was in contact with AT&T. "Should we learn of any malicious activity we will respond accordingly," an FBI spokesperson said.
AT&T apologized for the outage Thursday after several irate customers complained about being unable to make calls or send texts on social media.
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"We have restored wireless service to all our affected customers," the company said. "We sincerely apologize to them. 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."
Downdetector showed a spike in reported outages for T-Mobile and Verizon customers as well on Thursday, but both companies said their networks were operating normally and suggested customers were having trouble attempting to connect to users on other networks.
FOX Business' Pilar Arias, Louis Casiano and Fox News' Liz Friden contributed to this report.
