It appears that not all users have been affected by this problem there are people who are able to log in into the service. The Skype team said the following on their Twitter account

“Our engineers and site operations team are working non-stop to get things back to normal — thanks for your continued patience,” Luxembourg-based Skype said in a message on its Twitter feed @Skype.

In a blog post, Skype explained that computers known as “supernodes” had been taken offline by an unspecified 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.
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