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According to Microsoft,

To give some more detail, we were contacted by Skype about this last week and have worked to help them. First, we checked to see if there were any issues introduced by the security updates that could have caused the situation, and we found that there were no issues introduced by the security updates themselves.

Next, we checked with our Microsoft/Windows Update teams to see if there was anything unusual in this month’s update in terms of reboots, size of the updates or speed of distributing the updates through Automatic Update. We confirmed that there is nothing unusual in this month’s release that could have contributed to this situation. From a release point of view, this month’s release followed our usual format and processes.

Fortunately, Skype has identified the cause. As Villu Arak notes, “a previously unseen software bug within the network resource allocation algorithm” was the cause, and they have corrected it.

Skype noted is on its blog:

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.

Other Skype points of interest include:

On Thursday, 16th August 2007, the Skype peer-to-peer network became unstable and suffered a critical disruption. The disruption was triggered by a massive restart of our users’ computers across the globe within a very short timeframe as they re-booted after receiving a routine set of patches through Windows Update.

The 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.

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