Facebook has finally given a reason for the six-hour outage Monday

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Facebook stated in a blog post late Monday that the six-hour outage, which also affected Instagram, Messenger, Whatsapp, and OculusVR, was caused by a router configuration change, not a hack or effort to access user data.

While the initial explanation didn’t go into much depth, a second blog post on Tuesday did, claiming that the outage was caused by a regular maintenance error that effectively unplugged Facebook’s data centers from the internet.

Mark Zuckerberg, the company’s CEO, issued an apology on Monday evening, stating that the platforms would be restored. “I apologize for the inconvenience today; I understand how much you rely on our services to keep in touch with the people you care about.”

The outage began around 11:40 a.m. ET on Monday, causing severe issues for the organization. It was Facebook’s worst outage since January of this year when the service was down for more than 24 hours.

Employees were unable to contact one another via workplace message boards, and some told The Verge they were communicating using work-provided Outlook email accounts.

The issues spread to the servers that broadcast Facebook’s DNS and BGP information. Because of the failure, Facebook’s DNS routing information was lost, making it impossible for other networks to find its sites.

The interruption occurred only one day before Facebook whistleblower Frances Haugen was scheduled to testify before Congress about her experiences there.

Haugen, a former Facebook product manager who worked on the company’s Civic Integrity group, gave reporters at the Wall Street Journal access to a cache of internal Facebook papers.

On Sunday, she said on 60 Minutes that Facebook “pays for their profits with our safety.”