Facebook Inc. suffered a devastating outage that shut out many of its 2.7 billion global users, idled some of the company’s employees and prompted a public apology from the chief technology officer.

The company’s family of social-media apps, including the main social network, photo-sharing app Instagram and messaging service WhatsApp, began to return online for some users about 5:45 p.m. New York time, more than six hours after the incident began. It was one of the longest failures in recent memory. Downdetector, which monitors internet problems, said the Facebook outage is the largest it has seen, with more than 10.6 million reports worldwide.

Some internal services used by Facebook employees, including the company’s Workplace tool for communicating among teams, also had been knocked out for some staff, according to a spokesperson. Some workers were even struggling to use Facebook’s badge system at offices, according to a source familiar with the issues.

While it’s not uncommon for Facebook’s apps to have occasional glitches, technical issues that last more than a few minutes are rare. 

“*Sincere* apologies to everyone impacted by outages of Facebook powered services right now,” tweeted Chief Technology Officer Mike Schroepfer. “We are experiencing networking issues and teams are working as fast as possible to debug and restore as fast as possible.”

The outage was the latest in a series of difficult events for Facebook. A former employee turned whistle-blower appeared Sunday on CBS’s “60 Minutes” to accuse the company of prioritizing profits over user safety. The former employee, Frances Haugen, also handed over thousands of damning documents to U.S. lawmakers and the Wall Street Journal, which wrote a series of articles last month on Facebook’s struggles with content moderation and Instagram’s negative psychological impact on teenagers. The whistle-blower is also set to testify before a Senate subcommittee on Tuesday. 

Facebook shares dropped 4.9 per cent to US$326.23 at the close in New York. They had declined before the outage was reported, hurt by the whistle-blower’s “60 Minutes” appearance.

The outage Monday appeared to be related to Facebook’s DNS, or domain name system, records. Put simply, DNS converts domain names like “facebook.com” to the actual internet protocol addresses of the corresponding website. An error in DNS records can make it impossible to connect to a website. Facebook has had to physically reset some of the company’s servers in an effort to fix the problem.  

The cause of the issue is “probably a bad configuration or code push to the network management system,” said Alex Stamos, former chief security officer at Facebook who is now director of Stanford University’s Internet Observatory. “This isn’t supposed to happen.”

While the scale of the outage was unusual, Facebook’s internal apps stopped working for a time in 2019 following a dispute with Apple Inc., which halted some of the apps’ functionality on the iPhone maker’s platform.

After a user on Twitter suggested that Instagram should “stay offline forever,” Instagram boss Adam Mosseri jokingly replied, “Them fighting words… but it does feel like a snow day.”