Facebook along with its Instagram and WhatsApp platforms suffered a worldwide outage Monday that has extended more than three hours. Facebook's internal systems used by employees also went down. Service has not yet been restored.

The company did not say what might be causing the outage, which began around 11:40 a.m. ET. Websites and apps often suffer outages of varying size and duration, but hourslong global disruptions are rare.

"This is epic," said Doug Madory, director of internet analysis for Kentik Inc, a network monitoring and intelligence company. The last major internet outage, which k...