Internet phone service Skype revealed Monday that the three day service outage it experienced worldwide was caused by a "previously unseen software bug" that was triggered by Microsoft's regularly schedule monthly security update release. According to Skype's Villu Arak, the disruption started when Microsoft's monthly update caused Windows-based PCs around the globe to restart within a very short timeframe.

So is Arak actually blaming Microsoft for a Skype software error? Sort of. "The high number of restarts affected Skype's network resources," he writes in the Skype corporate blog. "This ... 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." Skype also verified that the outage had nothing to do with a malicious act of any kind.

The bug caused most Skype customers to lose access to the service for over 48 hours, though outages continued sporadically around the world for another day. Several million people are typically using the Skype service to make PC-to-PC and phone-to-PC calls at any time, and Skype reports that nearly 220 million have downloaded the software. About 50 million people regularly use the service.