Skype publicist Vilu Arak posted Skype's plain-language explanation of the Summer 2007 Skype Blackout to Skype's corporate blogs.

On Thursday, 16th August 2007, the Skype peer-to-peer network became unstable and suffered a critical disruption.

First Skype announcement: "Problems with Skype login."

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.

Was the "routine software update" from Microsoft or from Skype?

The abnormally high number of restarts affected Skype’s network resources.

So, fewer supernodes for a while? Each user starts as a node, and connects to the network before opting to act as a supernode. Connecting to the network...

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.

Too many nodes
chasing too few supernodes
nothing happens.

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.

If the bug was within the algorithm, in the Skype client, was the bug ever repaired?

If it was repaired, how was the fix propagated?

Regrettably, as a result of this disruption, Skype was unavailable to the majority of its users for approximately two days.

I'm eager to know more about the depth and expression of Skype's regret.

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.

That's good, no one to blame but Skype.

And the network is up.

Skype has not said:

1. If the no-self-healing bug is completely understood (just that it's been found)
2. If the bug is repaired (just that it's been found)
3. If the network collapse will not (cannot?) recur

The recovery may have been spontaneous; Skype hasn't posted anything to the contrary, nothing that says "we fixed the problem."