But the company said there was “no evidence that user data was compromised”.
The outage was the second blow to the social media giant in as many days after a whistleblower on Sunday accused the company of repeatedly prioritizing profit over clamping down on hate speech and misinformation.
Shares of Facebook, which has nearly 2 billion daily active users, opened lower after the whistleblower report and slipped further to trade down 5.3% in afternoon trading on Monday.
They were on track for their worst day in nearly a year, amid a broader selloff in technology stocks.