Facebook Inc.’s services went offline for as much as six hours Monday in an extended outage that disrupted access for users and businesses around the world and left the tech company flailing for a solution.

The company apologized for the outage, which affected its core platforms and apps including WhatsApp, Instagram, and Facebook Messenger—and which an outside tracking firm said appeared to be the most widespread in its history. Facebook said the problem was due to networking issues. Outside experts said it appeared to stem from a change the company made to networking instructions for access to its systems.

The disruption hobbled communication both essential and mundane, cut off small businesses from customers and slowed e-commerce across myriad countries. Some companies saw their operations and revenues curtailed, while others sent out marketing pitches based on the services going dark, underscoring the extent to which Facebook—despite the many controversies and challenges it faces—is at the center of daily life all over the globe.

In a blog post Monday night, Facebook blamed the outage on a configuration error. The outage cut off communications between Facebook’s data centers, leading to a cascade of disruptions as servers were cut off with each other, Facebook said. Internal systems were also hit, making it hard for the company’s engineers to diagnose and fix the problem, the company said. User data wasn’t compromised, according to the company. Facebook began restoring its networking services starting around 5:20 p.m. 

The outage appeared to have been the largest in the company’s history based on the number of users affected. It is the largest ever detected by Downdetector, which tracks website outages, with more than 10.6 million problem reports from around the world, according to a spokesman for Downdetector’s parent company.

Facebook Chief Executive Mark Zuckerberg apologized. “I know how much you rely on our services to stay connected with the people you care about,” he said in a Facebook post.

The outage comes at a time of scrutiny for the social media company. On Sunday, a whistleblower who provided documents that formed the foundation of The Wall Street Journal’s Facebook Files series went public. Frances Haugen, a former product manager at Facebook, said she acted to help prompt change at the company.

Facebook shares also dropped 4.9% on Monday amid a broad-market selloff. and it is now reported that FB CEO Mark Zuckerberg’s personal wealth fell by over $6 billion in a few hours after the outage bringing him down a notch on the list of the world’s richest people,