In a blog post put up late on 23 December, it said it was handling 90% of its typical call volume.
Audio, video and instant messaging systems that run over the Skype network were now running normally, it said.
Skype said the fault had been caused by a "software issue" on critical parts of its network.
"We take outages like this really seriously and apologise for the inconvenience," Skype chief Tony Bates told BBC News.
