Skype is down, in a worldwide outage that's lasted seventeen hours and counting for many users.
The problem seems to have been triggered by a recent software update, and has caused the failure of thousands of 'supernodes', which aggregate and route traffic. It's left millions of people worldwide unable to connect for voice, IM or video chat.
The problem was caused by the fact that, unlike a standard telephone network, Skype operates as a peer-to-peer network.
"Tt relies on millions of individual connections between computers and phones to keep things up and running. Some of these computers are what we call ‘supernodes’ – they act a bit like phone directories for Skype," the company explains on its blog.
"If you want to talk to someone, and your Skype app can’t find them immediately (for example, because they’re connecting from a different location or from a different device) your computer or phone will first try to find a supernode to figure out how to reach them."
The company says its engineers are working to create new 'mega-supernodes' to solve the problem, although it says that some features, such as video chat, will take longer to return to normal.
Enterprise products like Skype Connect and Skype Manager are unaffected, although the company warns that customers using the enterprise version of Skype for Windows may still experience delays signing in.
Skype's giving regular updates via Twitter, here. At about 3.30EDT the company said the system was returning to normal, but millions of users - including yours truly - are still unable to connect. We may have to wait a little longer, if past history is anything to go by - back in 2007, the company suffered an outage lasting two days.
A potentially enormous number of Skype's 124 million active users will have been counting on it to communicate with friends and family over the holiday period. Many more have become used to using it for business as a quick and easy way for remote staff to stay up to date, for inter-departmental communications and for videoconferencing.
This is bad timing for the company, which is looking to improve its profitability in preparation for an initial public offering next year.