Dallas-based AT&T's horrible, no good, very bad day

Thousands of Americans across the country were left without cell service Thursday after Dallas-based AT&T and other service providers encountered network outages.

Why it matters: The outages left customers unable to place calls, send texts or use the internet on their mobile phones, prompting safety warnings from authorities.

• The Federal Communications Commission confirmed Thursday afternoon that it is investigating the AT&T outage, according to CNN .

The latest: AT&T's network, which suffered the most widespread outages, was completely restored by early afternoon, the company said.

• "We sincerely apologize," the company said in a statement.

The big picture: North Texas was one of the hardest hit areas in the country, but outages were reported nationwide, including in Houston; Los Angeles; Chicago; Charlotte, North Carolina; and Atlanta.

The intrigue: Ravi Prakash, professor of computer sciences at University of Texas at Dallas, told FOX 4 that the outage could've been caused by a software patch.

• "Usually it is some kind of software bug that goes undetected and if you haven't properly tested it before release, it can have certain unforeseen outcomes," he said.

Zoom in: Tarrant County government said its services were affected by the outage .

What we're watching: Investigations into the cause of the outage could go on for a while.