A flaw in routine maintenance at Facebook’s network of data centres caused its global system to collapse for at least six hours on Monday, causing a host of problems that further delayed repairs, the social media company stated Tuesday.

The outage was the largest ever seen by web monitoring firm Downdetector, blocking access to apps for billions of Facebook, Instagram and WhatsApp users, intensifying weeks of scrutiny for the nearly $1 trillion technology giant.

Santosh Janardhan, Facebook’s vice president of engineering, reasoned the company’s engineers had issued an order unintentionally disconnecting Facebook’s data centers from the rest of the world.

Facebook’s systems are designed to check commands to prevent errors, but the verification tool had an error and would not block the command that caused the outage.

While users have lost access to one of the most popular messaging apps on the planet – WhatsApp has more than 2 billion users – employees have also been blocked from using internal tools.

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