If you’re a frequent Skype user, you probably noticed, or heard about, a massive outage that the service was experiencing last week. In a blog post today, the VoIP company’s CIO, Lars Rabbe, explained exactly what happened to cause the interruption.
On Wednesday, December 22, a cluster of support servers responsible for offline instant messaging became overloaded. As a result of this overload, some Skype clients received delayed responses from the overloaded servers. In a version of the Skype for Windows client (version 5.0.0152), the delayed responses from the overloaded servers were not properly processed, causing Windows clients running the affected version to crash.
Users running either the latest Skype for Windows (version 18.104.22.168), older versions of Skype for Windows (4.0 versions), Skype for Mac, Skype for iPhone, Skype on your TV, and Skype Connect or Skype Manager for enterprises were not affected by this initial problem.
However, around 50% of all Skype users globally were running the 22.214.171.124 version of Skype for Windows, and the crashes caused approximately 40% of those clients to fail. These clients included 25–30% of the publicly available supernodes, also failed as a result.
Along with its official mea culpa, Skype has begun sending emails to some of the affected users offering a $1 service credit. Skype asserts that it has taken measures to prevents such an outage from happening again.