What Happened at Skype

A "routine software update" destabilized Skype's peer-to-peer IP telephony network, triggering computer restarts that disrupted the service for two days, the company said last night in a long-awaited explanation of its recent troubles. "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," the company said. "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."

Skype doesn't identify the update, but the Register says it was the monthly Microsoft security patches that were deployed last Tuesday. Since Microsoft has been issuing its monthly "Black Tuesday" security patches for years, and these updates usually require system reboots, it's not at all clear why this month's updates would be any different.

While this wasn't a data center failure, the particulars of Skype's difficulties will be of interest to those tracking peer-to-peer networks, and offer an additional example for the "how stuff breaks" library.