US Telecom company AT&T - the largest in the country, with more than 240 million subscribers - apologized to its customers for the hours-long outage on Thursday (Feb. 22), explaining that the issue was a result of a technical error and not a malicious cyberattack.
The outage knocked out cellphone service for thousands of its users across the US before it was eventually restored.
Outage tracker Downdetector noted that the outage began at about 03:30 Eastern Time (08:30 UTC) and peaked at around 73,000 reported incidents. Around noon ET, AT&T had more than 58,000 outages in locations including Houston, Atlanta, and Chicago.
By 21:00 ET (02:00 UTC), the reports on AT&T's network dwindled to fewer than 1,000.
Cricket Wireless, which AT&T owns, had more than 9,000 outages at one point, but the reports had also tailed off later in the afternoon.
Users of other carriers, including Verizon and T-Mobile, also reported issues but said that their networks were operating normally and that the problems were likely stemming from customers trying to connect to AT&T users, the Associated Press reported.
AT&T: Outage Not Caused by Cyberattack
In a statement, the Dallas-based company blamed the incident on an error in coding but fell short of elaborating why.
"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," the company said in its latest update. "We are continuing our assessment of today's outage to ensure we keep delivering the service that our customers deserve."
The Federal Communications Commission (FCC) contacted AT&T about the outage, and, according to National Security Council spokesman John Kirby, the Department of Homeland Security and the FBI were also investigating the matter.
Comments coming from Capitol Hill also meant they were not convinced of AT&T's explanation.
"We are working to assess today's disruption in order to gain a complete understanding of what went wrong and what can be done to prevent future incidents like this from occurring," Republican Representative Cathy McMorris Rodgers (WA) of the House Energy and Commerce Committee and Rep. Bob Latta (OH) of the Communications and Technology Subcommittee said in a statement.
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