A nationwide cellular outage affecting hundreds of thousands of customers on Thursday was the result of an error, not a cyber attack, AT&T has revealed

AT&T customers woke up unable to make calls or access the Internet, a condition that lasted until early afternoon before service was finally restored

A spokesperson for the company stated that this was the result of an error that occurred during a network expansion and that they would continue to evaluate the issue

Initial reports came in early in the morning, with some 70,000 customers expressing concerns on the outage reporting site Downdetector

While there were hotspots of reported problems in Atlanta, Chicago, Dallas, Houston, and Los Angeles, access issues continued throughout the morning on the East Coast

Other operators, including Verizon and T-Mobile, also reported problems, which appear to be related to trying to reach AT&T customers

Fortunately, AT&T's network outage was not prolonged By late afternoon, the company issued a statement that service had been fully restored However, the cause of the network outage is still unknown, and the FCC will be investigating the issue

In the early days of the outage, there was much speculation about the cause, with some pointing to the possibility of a cyber attack or solar flare While these are usually harmless, solar flares can significantly disrupt cellular communications

National Security Council spokesman John Kirby said both the FBI and the Department of Homeland Security are looking into the outage

Specific details from AT&T are fairly limited, but the company said its network expansion efforts resulted in an error, which caused Thursday's massive outage

AT&T eventually issued a short statement explaining: "Based on our initial investigation, we believe that today's outage was caused by the application and execution of an unauthorized process used during the network expansion, rather than a cyber attack

Adding: "We are continuing to evaluate today's outage in order to continue to provide our customers with the service they deserve