Facebook said on Tuesday that routine maintenance on the company's network stitching together its data centers triggered the collapse of its global system for more than six hours on Monday, blocking access for billions of users.
In a blog post, Facebook explained its engineers issued a command that unintentionally took down all the connections in its network, "effectively disconnecting Facebook data centers globally."
The outage cut off access to Facebook, Instagram and WhatsApp globally.
It also caused employees to lose access to internal tools, including those used by Facebook employees to correct such issues, the company said.
Facebook added that its program audit tool had a bug, and failed to stop the command that caused the outage.