Caused by compatibility issues with some versions of Skype, a large number of “supernodes” were interpreted as offline resulting to a large number of Skype users today to greatly deplete. Skype responds to the downtime problem with “mega-supernodes.”

Skype’s network is dependent on individual connections between computers and phones for its operation. A number of these computers are labeled as ‘supernodes’ which functions similar to phone directories. If Skype is unable to find the person you talk to because of location or device shift, your computer or phone will locate a supernode that will connect to them the fastest.

From the Skype blog:

“Earlier today, we noticed that the number of people online on Skype was falling, which wasn’t typical or expected, so we began to investigate.

Skype isn’t a network like a conventional phone or IM network – instead, it 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. 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.

Under normal circumstances, there are a large number of supernodes available. Unfortunately, today, many of them were taken offline by a problem affecting some versions of Skype. As Skype relies on being able to maintain contact with supernodes, it may appear offline for some of you.

What are we doing to help? Our engineers are creating new ‘mega-supernodes’ as fast as they can, which should gradually return things to normal. This may take a few hours, and we sincerely apologise for the disruption to your conversations. Some features, like group video calling, may take longer to return to normal.

Stay tuned to @skype on Twitter for the latest updates on the situation – and many thanks for your continued patience in the meantime.”

Skype’s last big outage was in 07. The company announced it would last for about 12-24 hours, an insane amount of time for a downtime considering that it’s a communications company that will cause transactions to stop for a day.