The Oct. 4 outage appeared to be occurring primarily in urban areas, and even extended to Facebook employees themselves, who reportedly weren’t able to enter company buildings with their badges. The issue appears to be linked to the Domain Name System, which translates domain names to IP addresses and stopped directing users to the correct website, according to Reuters. Security experts say the outage was likely triggered by a “configuration error” resulting from an internal mistake, although it’s theoretically possible an employee could have tampered purposefully with the system. It’s unlikely that it was the result of an external attack.

Facebook, Instagram, and WhatsApp count more than 6 billion users worldwide, including users who subscribe to multiple services, according to recent company estimates. The watchdog organization NetBlocks said it was the most severe outage on record to affect Facebook.

Global outages of this scale are relatively rare, but not unheard of. Last December Google suffered a major outage that caused apps like Gmail and Maps to crash, and in June the cloud computing company Fastly’s servers went down for half an hour blocking access to sites like the Guardian, the New York Times, and Reddit.

Outage comes amidst reckoning over Facebook products

Facebook’s platforms crashed just as the company is facing scrutiny over a Wall Street Journal investigation revealing the company has for years conducted internal research about the negative effects its products have on users without taking significant steps to address these issues.

The company was aware, for example, that teen users linked suicidal thoughts directly to Instagram, but reportedly only took small actions—such as hiding the platform’s “like” feature—in response to these concerns. Following revelations from the Journal investigation, Facebook halted its rollout of a version of Instagram designed for kids under the age of 13.

Facebook stock dropped by 5.3% amid the outage which comes a day after whistleblower Frances Haugen, who used to work for the company’s Civic Integrity team, told CBS’s 60 minutes why she decided to leak the internal reports, saying, “the version of Facebook that exists today is tearing our societies apart and causing ethnic violence around the world”. There was no indication as of Monday afternoon that the outage was linked to concerns over Facebook’s conduct as a business.

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