Facebook, Instagram and WhatsApp suffered a global outage. What happened?

Some of Facebook, Instagram and WhatsApp’s more than 2 billion users were unable to access the online services from Wednesday until Thursday afternoon as the social network and its sister apps suffered a prolonged outage.
“We’re very sorry for the inconvenience and appreciate everyone’s patience,” Facebook said.
Facebook confirmed on Twitter that its suite of apps were offline for some users, stemming from server issues. But the company said Thursday that it has fixed the problem and that its systems are “recovering.”
On Wednesday, Facebook dispelled speculation that the outage was caused by a denial-of-service attack (DDoS), a type of cyberattack that disrupts an online service by flooding it with requests. Facebook said it was working to resolve the issue but didn’t announce the fix until Thursday.
Before Facebook’s latest update, Instagram came back online. On Twitter, the company posted a GIF of a jubilant Oprah Winfrey, exclaiming, “Anddddd . . . we’re back”