Facebook is suffering from an outage, the website has been down for more than an hour already for users worldwide. Some users report they can't login anymore. Also Instagram appears to be unreachable.
Users complain on Twitter about both the Facebook and Instagram downtime, but not everyone appears to be affected.
The cause of the outage is unknown. The Facebook Status page so far only shows an issue that started yesterday, a Facebook engineer reports, "Real Time Updates are currently operating in a degraded state. Update notifications may be delayed. Our engineers are working on this issue and will have it resolved as soon as possible."
Update: Both Facebook and Instagram are fully up again
