Hey guys, thank you for raising this to us. We're currently investigating this issue as an immediate priority. We will let you know as soon as it's fixed. Really sorry for the inconvenience caused.
EDIT: Servers are coming back online, most players will be able to login and we'll have the remaining ones online again as soon as possible. I would advise to not do any risky content just yet because we'd like to ensure all the servers are OK.
EDIT 2: We see reports of worlds going offline again, it's being investigated. Again we are really sorry for this.