Watch: ‘Faulty configuration change’ to blame for outage, Facebook says
Facebook has blamed a "faulty configuration change" for an outage that prevented the company's 3.5 billion users from accessing its apps and services, including Whatsapp and Instagram, for nearly six hours.
The platforms crashed on Monday afternoon, with users unable to send or receive messages or refresh their news feeds.
In a Facebook post after the service had been restored, chief executive Mark Zuckerberg wrote: "Facebook, Instagram, WhatsApp and Messenger are coming back online now.
"Sorry for the disruption today - I know how much you rely on our services to stay connected with the people you care about."
Security experts have said an inadvertent mistake or sabotage by an insider were both plausible reasons for the unprecedented outage.
Facebook said: "To all the people and businesses around the world who depend on us, we are sorry for the inconvenience caused by today's outage across our platforms.
"We've been working as hard as we can to restore access, and our systems are now back up and running.
"The underlying cause of this outage also impacted many of the internal tools and systems we use in our day-to-day operations, complicating our attempts to quickly diagnose and resolve the problem.
"Our engineering teams have learned that configuration changes on the backbone routers that coordinate network traffic between our data centres caused issues that interrupted this communication.
"This disruption to network traffic had a cascading effect on the way our data centres communicate, bringing our services to a halt.
"Our services are now back online and we're actively working to fully return them to regular operations.
"We want to make clear at this time we believe the root cause of this outage was a faulty configuration change.
"We also have no evidence that user data was compromised as a result of this downtime."
Problems were reported across the world, including in North and South America, Europe, Australia, Russia, and New Zealand.
People using their Facebook credentials to log in to third-party apps such as Pokemon Go and Match Masters were also said to be facing issues.
For hours, Facebook's only public comment was a tweet in which it acknowledged that "some people are having trouble accessing (the) Facebook app" and said it was working on restoring access.
Regarding the internal failures, Instagram head Adam Mosseri tweeted that it feels like a "snow day".
"Facebook basically locked its keys in its car," tweeted Jonathan Zittrain, director of Harvard's Berkman Klein Center
for Internet & Society.
Sky's US correspondent Greg Milam, at Facebook HQ in California, said: "Even when it started to get back to normal it was very, very slow and sporadic before people had everything back up and running.
'It's not just about posting pictures and status updates. For hundreds of thousands of people around the world this was about their ability to do business.
"They run their businesses through Facebook. Whatsapp has two billion users - for many of those people it is their only form of communication and they felt very vulnerable without that and without the ability to do business.
"It shows how much Facebook is now part of critical infrastructure in the US and around the world."
Twitter and Tik Tok reported higher-than-normal usage, which led to some issues in people accessing Twitter posts and direct messages.
Shares of Facebook, which has nearly 2 billion daily active users, closed 4.9% lower on Monday, wiping $47bn (£34.5bn) off its market value.
The company is already in the throes of a separate major crisis after whistleblower Frances Haugen, a former Facebook product manager, provided The Wall Street Journal with internal documents that exposed the company's awareness of harms caused by its products and decisions.
Ms Haugen went public on CBS's 60 Minutes programme on Sunday and is scheduled to testify before a Senate subcommittee on Tuesday.
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