Facebook service slowly returns online after one of the biggest blackouts in memory recently. Facebook, Instagram, Whatsapp and Messenger applications seem to work again, although some websites load it slower than usual.

At 6:05 PM ET Monday, the “Facebook for business status” page still shows “big interference,” to the core social networking service. But it is still an increase from the beginning of the day when the website is fully offline.

“To the large community of people and businesses around the world that depend on us: Sorry,” Facebook wrote in a statement posted to Twitter. The company confirms the service “will return online now.” In a post on Facebook, CEO Mark Zuckerberg also apologized for the service down.

Zuckerberg does not describe the cause of longing. In the previous tweet, the company head out of the company, Michael Schroepfer, quoted “network problems.”

Blackouts lasts more than six hours, records Instagram, WhatsApp, Messenger and Oculus. It also brought havoc in the company internally, with employees reportedly unable to access e-mail, workplaces and other tools. The New York Times reports that employees are also physically locked from the office as a badge of workers stop working.

It also shaved billions of dollars from Zuckerberg’s private net worth as Facebook shares, Bloomberg reported. Elsewhere, the company is still shaken from the fall of the Whistleblower that accuses the company prioritizing “profit for salvation.” Whistleblower is the main source of Wall Street Journal for several articles that detail how Dangerous Instagram and the “Cross Check” program is controversial companies that allow high-profile users to break the rules.

Brian Krebs Security Reporter reports blackouts linked with problems with BGP (Border Gateway Protocol) Facebook, which prevents company service accessible. He then added it was “Routine BGP update wrong.” DNS CloudFlare provider also quotes BGP as the possibility of the perpetrators, writing in a blog post that it is “as if someone has ‘pull the cable’ from their data center at once and disconnected from the internet.”

Late on Monday night, the Facebook engineering team published a blog post that tried to explain what happened:

“Our technical team has learned that configuration changes in the backbone router that coordinates network traffic between our data centers causing problems that interfere with this communication. This disorder to network traffic has a cascading effect on the data center we communicate, bring our services to stop. “

It continues by saying that the root causes of blackouts are “wrong configuration changes” and there is no evidence that the user data is compromised because of downtime.