According to a notice just posted by Villu Arak on the Skype blog, a high number of restarts after a routine software update caused the nearly two-day sign-in outage last week.
Plus, they are saying it won't happen again.
Here's the official scoop from Villu:
On Thursday, 16th August 2007, the Skype peer-to-peer network became unstable and suffered a critical disruption. The disruption was initiated by a massive restart of our user’s computers across the globe within a very short timeframe as they re-booted after receiving a routine software update.
The abnormally high number of restarts affected Skype’s network resources. This caused a flood of log-in requests, which, combined with the lack of peer-to-peer network resources, prompted a chain reaction that had a critical impact.
Normally Skype’s peer-to-peer network has an inbuilt ability to self-heal, however, this event revealed a previously unseen software bug within the network resource allocation algorithm which prevented the self-healing function from working quickly. Regrettably, as a result of this disruption, Skype was unavailable to the majority of its users for approximately two days.
The issue has now been identified explicitly within Skype. We can confirm categorically that no malicious activities were attributed or that our users’ security was not, at any point, at risk.
This disruption was unprecedented in terms of its impact and scope. We would like to point out that very few technologies or communications networks today are guaranteed to operate without interruptions.
We are very proud that over the four years of its operation, Skype has provided a technically resilient communications tool to millions of people worldwide. Skype has now identified and already introduced a number of improvements to its software to ensure that our users will not be similarly affected in the unlikely possibility of this combination of events recurring.
The Skype community of users has been incredibly supportive and we are very grateful for all their good wishes.