Skype Explains It’s Recent Outage…. Blame The Buggy Software

In a blog posting today, Skype Chief Information Officer Lars Rabbe explained what happened in regards to that outage that hit the VoIP service recently. Apparently, it was due to a particular version of Skype for Windows that was to blame:

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, 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 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 of this problem.

Lovely. He also explained how they would avoid this in the future:

First, we will continue to examine our software for potential issues, and provide ‘hotfixes’ where appropriate, for download or automatic delivery to our users. Since a bug was identified in Skype for Windows (version, we had provided a fix to v5.0 of our Windows software prior to the incident, and we will provide further updates for download this week. We will also be reviewing our processes for providing ‘automatic’ updates to our users so that we can help keep everyone on the latest Skype software. We believe these measures will reduce the possibility of this type of failure occurring again.

Second, we are learning the lessons we can from this incident and reviewing our processes and procedures, looking in particular for ways in which we can detect problems more quickly to potentially avoid such outages altogether, and ways to recover the system more rapidly after a failure.

Third, while our Windows v5 software release was subject to extensive internal testing and months of Beta testing with hundreds of thousands of users, we will be reviewing our testing processes to determine better ways of detecting and avoiding bugs which could affect the system.

Finally, as we continue to grow, we will keep under constant review the capacity of our core systems that support the Skype user base, and continue to invest in both capacity and resilience of these systems. An investment program we initiated a year ago has significantly increased our capacity already and more investment is planned for 2011 both to support the ongoing roll out of our paid and enterprise products, and to continue to support the growth of our core Skype software that we know millions of users rely on every day.

We’ll see if that pans out. If that isn’t enough to keep you happy, a credit of $1 is being e-mailed to Skype users. I know this because I got one of these e-mails. Now $1 doesn’t sound like a lot. But in Skype terms, it’s a big credit. This is what the e-mail said:

To our valued customers:

As 2010 draws to a close, I would like to take a moment to thank each of you for your patience, understanding, and support during Skype’s recent outage.

We know how important your Skype conversations are to you and we take any disruption to our service very seriously. We are pleased to confirm that Skype is back to normal allowing you to connect with friends, co-workers, family and loved ones.

As a valued customer of Skype, we would like to offer you a sincere apology and offer you our gratitude with a credit voucher worth a call of more than 30 minutes to a landline in some of our most popular countries, such as USA, UK, Germany, China, Japan. Or spend it however you like on Skype…

Thank you for allowing us at Skype to be a part of your life. May your holidays and the New Year be a time of joy, peace, and health for you and your family.

At least they realize how important Skype is for many people worldwide. Let’s hope this never happens again.

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