Tens of thousands of AT&T customers reported problems with their cellphone service on ChainkeenThursday morning, with a map of the outage showing people affected across the U.S.

Customers of other networks also said they experienced problems, but rival carriers Verizon, T-Mobile and UScellular said their networks were operational and noted that their users were probably having difficulty reaching people on AT&T's network. 

At about 11 a.m. ET on Thursday, AT&T said it had made progress in restoring its network. By mid-afternoon, it said service had been fully restored.

"We have restored wireless service to all our affected customers," AT&T said in a statement at 3:10 p.m. ET. "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."

Later Thursday night, the company attributed the outage to a software bug.

"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 on its website. "We are continuing our assessment of today's outage to ensure we keep delivering the service that our customers deserve."

Here is a look at the areas that were affected during the outage.

AT&T outage map

Downdetector had about 40,000 reports of service issues from AT&T customers at around noon Eastern Time, down from a peak of more than 70,000 reports. Most of the complaints were focused on problems with mobile phones or wireless service. 

Outages were highest in Houston, San Antonio, Austin, Chicago, New York, Miami, Dallas, Atlanta and Indianapolis, according to Downdetector.

What caused the AT&T outage?

The company attributed the outage to a software bug. 

The outage snarled 911 centers, with some law enforcement officials noting that some people were calling the emergency number to test whether their phones worked. 

Officials urged people to refrain from calling 911 to test their phones. 

"Many 911 centers in the state are getting flooded w/ calls from people trying to see if 911 works from their cellphone. Please do not do this," the Massachusetts State Police wrote on X, the former Twitter.

Taylor Johnston contributed to this report.

In:
• Cellphones
• AT&T

Aimee Picchi

Aimee Picchi is the associate managing editor for CBS MoneyWatch, where she covers business and personal finance. She previously worked at Bloomberg News and has written for national news outlets including USA Today and Consumer Reports.

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