Facebook is back online after an outage Monday left millions of people around the world unable to use it, along with its Instagram and WhatsApp platforms.
Facebook users said Monday evening that they could regain access to the site, about six hours after it went down.
The company later confirmed on Twitter that the platform was accessible: "We've been working hard to restore access to our apps and services and are happy to report they are coming back online now."
Facebook added: "To the huge community of people and businesses around the world who depend on us: we're sorry. … Thank you for bearing with us."
The outage began shortly before noon Eastern Daylight Time. Thirty minutes later, Facebook tweeted, "We're aware that some people are having trouble accessing our apps and products. We're working to get things back to normal as quickly as possible, and we apologize for any inconvenience."
Facebook officials have not said what caused the problem. However, cybersecurity experts said that online routes leading users to Facebook's platforms were disrupted. Since Facebook controls those routes, the experts said, the problem was likely an internal issue.
There was no evidence of malicious activity, according to Web security company Cloudflare. Its CEO, Matthew Prince, tweeted: "Nothing we're seeing related to the Facebook services outage suggests it was an attack."
Cloudflare said in a blog post that Facebook had "reconnected to the global internet" by Monday evening but that it would take time for all of Facebook's services to be running smoothly.
Mike Schroepfer, Facebook's chief technology officer, tweeted earlier Monday, "We are experiencing networking issues, and teams are working as fast as possible to debug and restore as fast as possible."
Facebook employees reported they lost access to some of their own tools Monday, making the company's response more difficult.
Instagram head Adam Mosseri tweeted that it "feels like a snow day."
Some information in this report came from The Associated Press, Reuters and Agence France-Presse.
