Facebook has claimed the 14-hour outage on Wednesday (13.03.19) was due to a server configuration change.
The social network's company of apps, Facebook, Facebook Messenger, WhatsApp and Instagram all went down for the lengthy amount of time and now the firm has explained why.
They said: "As a result of a server configuration change, many people had trouble accessing our apps and services.
"We've now resolved the issues and our systems are recovering."
However, they didn't divulge what severe change they carried out to cause the blackout.
It was the worst outage in all 15 years of Facebook.
The apps stopped working at around 4pm.
Mark Zuckerberg's company were forced to address the blackout on rival site Twitter.
They wrote: "We're aware that some people are currently having trouble accessing the Facebook family of apps. We're working to resolve the issue as soon as possible."
They also denied reports that the outage was due to an attack from a Distributed Denial of Service (DDoS), which occurs when multiple systems flood the bandwidth or resources of a targeted system, usually one or more web servers.
They added: "We're focused on working to resolve the issue as soon as possible, but can confirm that the issue is not related to a DDoS attack."
There had been reports that it was knocked out by a Border Gateway Protocol (BGP) leak from a European internet service provider to a major transit ISP.
Roland Dobbins, the Principal Engineer of the network performance company Netscout, said: "While not malicious in nature, such events can prove disruptive on a widespread basis. It is very important that all network operators implement BGP peering best current practices."
In 2018, a similar thing happened when Facebook went down for 40 minutes, due to a "routine test".
The social network left many users in the US and other parts of the world unable to access their accounts for almost an hour, but didn't explain what they were testing.
A spokesperson for the company said at the time: Earlier today, a routine test caused users to have trouble accessing or posting to all Facebook services including WhatsApp and Instagram.
"We quickly investigated and restored access for everyone. We're sorry for the inconvenience."
People in Brazil, Peru and Mexico were among those affected.
They also had problems accessing Facebook-owned apps WhatsApp and Instagram.