The voice over IP provider, which delivers free and cut-price IP-based phone calls, has acknowledged the problems and says its engineers are working to fix the log-in problems customers are facing.
Skype told customers in a service update: "Some of you may be having problems logging into Skype. Our engineering team has determined it is a software issue and hopes to have this resolved quickly.
"Meanwhile, you can simply leave your Skype client running and as soon as the issue is resolved, you will be logged in. We apologise for the inconvenience."