AT&T service restored after customers hit by widespread cellular outages in the U.S.

AT&T’s widespread outage that left thousands without service for hours Thursday was likely caused by a process error — not a cyberattack, the carrier said.

The trouble started early Thursday, but by afternoon AT&T reported that service had been restored to all customers.

Based on an initial review, the company thinks the outage "was caused by the application and execution of an incorrect process used as we were expanding our network, not a cyber attack," it said Thursday evening.

Over 32,000 AT&T outages were reported by customers about 4 a.m. ET Thursday. Reports dipped then spiked again to more than 50,000 around 7 a.m., with most issues reported in Houston, Chicago, Dallas, Los Angeles and Atlanta, according to the site.

That number surged to more than 71,000 just before 8 a.m. ET.