Facebook, along with its Instagram platform and WhatsApp platform, suffered a global outage Monday that lasted more than three hours. The downtime also affected employees’ access to internal Facebook systems. Service has not been restored yet.

The cause of the outage that began at 11:40 a.m. was not yet known by the company. ET. Websites and apps can sometimes experience outages of varying duration and size, but it is rare to experience long-lasting global disruptions.

Doug Madory is Kentik Inc’s director of internet analysis. He said that “this is amazing.” The most recent major internet outage in June knocked down many of the top websites around the globe. It lasted less than one hour. Fastly, a content-delivery company, blamed the outage on a software glitch that was triggered by a customer changing a setting.

Facebook’s most public comment was a tweet, in which it acknowledged that some people were having difficulty accessing the Facebook app and said that it was working to restore access. Instagram’s head Adam Mosseri said that the experience feels like “snow day” in light of the internal problems.

However, the impact was much worse for Facebook’s almost 3 billion users. This shows how dependent the world is on Facebook and its properties. It can be used to run businesses, connect to affinity communities, log onto multiple websites, and even order food.

It also demonstrated that no other platform can replace the social network that has grown over 17 years to be all-important infrastructure. Facebook’s Monday request that the Federal Trade Commission dismiss a revised antitrust case against it because it is facing fierce competition from other services rang a little hollow.

It is not clear what caused the outage. Madory stated that it seems like Facebook created “authoritative DNS routing” to allow the rest of the internet to communicate with its properties. These routes are part the internet’s Domain Name System (a central component that directs its traffic). Apps and web addresses would not be able to locate the route without Facebook posting it on the internet.

Many people rely on Facebook, WhatsApp, or Instagram for their primary communication channel. Losing access for this long could make them vulnerable to criminals, according Rachel Tobac, hacker and CEO at SocialProof Security.

She said that people don’t know how they can contact their loved ones without social engineering. “They are more vulnerable to social engineering because it is so urgent to communicate,” Tobac stated. In the past, people received emails promising to restore social media accounts by clicking on malicious links that could expose their personal information.

Chief technical officer at cybersecurity firm BreachQuest Jake Williams said that although foul play cannot always be ruled out it is possible that the outage was caused by human error.

Madory stated that there was no evidence that Facebook was to blame and dismissed the possibility of another internet company (e.g., a telecom company) having inadvertently changed major routing tables that impact Facebook.

Madory stated, “No other person has announced these routes.”

Computer scientists suspect that the bug could have been introduced through a configuration change in Facebook’s routing management system. Steven Bellovin, a computer scientist at Colombia University, tweeted that he believed Facebook would attempt an automated recovery in such cases. He said that if this fails, Facebook could be in for “a lot of pain” because it would have to make manual changes at external data centers.

Bellovin tweeted, “What it boils to is that running a large, even by Internet standards distributed system, is very difficult even for the best.”

Facebook was already facing a major crisis. Frances Haugen (a former Facebook product manager) provided The Wall Street Journal internal documents that revealed the company’s knowledge of the harms its products and decisions caused. Haugen made his public appearance on CBS’s “60 Minutes” Sunday. He is due to testify before the Senate subcommittee on Tuesday.

Haugen also filed anonymous complaints with federal law enforcement alleging that Facebook’s own research has shown how it magnifies hatred and misinformation, leads increase polarization, and that Instagram can harm teenage girls’ mental well-being.

The Journal’s “The Facebook Files” stories painted a picture that shows a company that is more concerned with growth than the public good. Facebook tried to minimize the impact of the research. In a memo to Facebook employees, Nick Clegg (the company’s vice-president of policy and public affairs) stated that social media had “a huge impact on society in the recent years and Facebook is often a venue where much of this discussion plays out.”

Twitter, however, posted “hello literally everybody” from its main Twitter account as jokes and memes regarding the Facebook outage flood the platform. Later, a unverified screenshot suggesting that facebook.com was up for sale circulated, Jack Dorsey, CEO of Twitter, tweeted “how much?”