Thousands of AT&T customers across the country woke up Thursday morning without service — leaving them with no access to text messaging, internet and phone calls for hours.

Right now, AT&T isn’t saying exactly what caused the outage but says service was restored late Thursday afternoon, leaving customers with more questions than answers.

Like many AT&T customers, University of Rochester student Eva Liu was surprised to hear about the service outage.

“I realized someone posted on Instagram and was like, oh, AT&T out of service this morning,” she said. But by then, she says service had been restored to her phone. “I woke up too late to realize anything like that, so I didn’t really realize until my friends were like, oh, AT&T is out of service.”

According to AT&T, more than 42,000 customers lost service around 4:30 a.m. Thursday, then another wave surged the number of customers without service to 71,000 by 8 a.m. — leaving some to speculate that overnight solar flares could have caused the outage.

But according to Rochester Institute of Technology research engineer Serena Flint, that isn’t likely. She says solar flares typically impact areas of the Earth where the sun is shining.

” I should note that the solar flare is not actually related to it,” she said. In the case of a solar flare, she said, “we would actually expect to be seeing the greatest impact in parts of India, China, Australia.”

The lead AT&T communications manager for the Rochester area confirmed in a statement to News10NBC that: “We have restored wireless service to all our affected customers. 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.”

Welcome news to customers like Liu.

Although no explanation has been provided by the telecom giant, the U.S. Cybersecurity and Infrastructure Security Agency said Thursday afternoon there is no indication that this was a cyber attack.

The Federal Communications Commission, the FBI and the Department of Homeland Security are lending a hand in the investigation.