Just as Facebook’s Antigone Davis was live on CNBC defending the company over a whistleblower’s accusations and its handling of research data suggesting Instagram is harmful to teens, its entire network of services suddenly went offline.

The outage started just before noon ET and took nearly six hours before it was resolved. This is the worst outage for Facebook since a 2019 incident took its site offline for more than 24 hours, as the downtime hit hardest on the small businesses and creators who rely on these services for their income.

Facebook issued an explanation for the outage on Monday evening, saying that it was due to a configuration issue. On Tuesday afternoon, Facebook engineers offered more detail, explaining that the company’s backbone connection between data centers shut down during routine maintenance, which caused the DNS servers to go offline. These two factors combined in making the problem more difficult to fix, and they help explain why services were offline for so long.

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