Millions of people around the globe have been hit by an outage at the popular internet phone service Skype. Users as far afield as Japan, Europe and the US have all reported problems.

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. However, on Wednesday, 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 appeared offline for some users.

Skype said that its 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," Skype said.