Facebook CEO Mark Zuckerberg has used the platform to apologise for the outage that took down Facebook, WhatsApp, Instagram and Messenger globally for just under six hours yesterday. It was the company’s worst outage since 2008, and wiped almost $40bn off Facebook’s value.

In a Facebook post, 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.”

Separately, Santosh Janardhan, VP Engineering and Infrastructure at Facebook posted an apology on the Facbook blog in which he revealed that the underlying cause of the outage also impacted many of the internal tools and systems Facebook uses in its day-to-day operations, complicating the company’s attempts to quickly diagnose and resolve the problem. It has been reported that Faceboo staff were unable to access their company email, or even gain access to some parts of their offices.

Janardhan wrote: “Our engineering teams have learned that configuration changes on the backbone routers that coordinate network traffic between our data centers caused issues that interrupted this communication. This disruption to network traffic had a cascading effect on the way our data centers communicate, bringing our services to a halt…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…We apologize to all those affected, and we’re working to understand more about what happened today so we can continue to make our infrastructure more resilient.”