AT&T Outage Triggered by Company Work on Network Expansion

(Bloomberg) — AT&T Inc. said a widespread outage that took hours to resolve Thursday was caused by “an incorrect process” while expanding the wireless network.

Most Read from Bloomberg

The software issue interrupted wireless service for hundreds of thousands of subscribers and prompted the FBI and US Department of Homeland Security to investigate the outage.

“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,” an AT&T spokesman said in a statement. “We are continuing our assessment of today’s outage to ensure we keep delivering the service that our customers deserve.”

AT&T said all wireless service was restored Thursday afternoon, capping a day of frustration that began in the early hours of the morning New York time. AT&T customers filed more than 1.5 million outage reports on service-tracking website Downdetector.

The federal government began investigating whether the network failure was caused by a cyberattack, according to two US officials familiar with the situation, who requested anonymity to discuss sensitive information.

The Federal Communications Commission also has been in touch with AT&T to try and ascertain the cause, White House spokesman John Kirby told reporters earlier. “DHS and the FBI are looking into this as well, working with the tech industry, these network providers, to see what we can do from a federal perspective to enhance their investigative efforts to figure out what happened here,” Kirby said.

Read More: AT&T Outage Turns Start of US Workday Into the ‘Apocalypse’

Story continues

Early Thursday, mobile-phone customers from multiple carriers started reporting problems, but it soon became clear that AT&T’s network was the culprit. Outages were reported from cities including New York, Houston, Atlanta, Miami, Chicago and Dallas. The service disruption upended communications with…