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Microsoft Pri0

Welcome to Microsoft Pri0: That's Microspeak for top priority, and that's the news and observations you'll find here from Seattle Times technology reporter Matt Day.

August 20, 2007 at 12:21 PM

Skype ties outage to Windows security update, faulty algorithm

Skype implicated Microsoft security updates for the outage that left millions without their Internet phone service. The company had earlier faulted “a deficiency in an algorithm within Skype networking software,” and ultimately acknowledged that its own software was at fault.

A Skype employee, posting to a public company blog that details the status of its service, explained the outage that began on Thursday:

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.

Microsoft releases security updates for its software on the second Tuesday of every month — “patch” Tuesday. On Aug. 14, the company released nine patches, six of which were considered critical. Microsoft told The Associated Press that it was a routine patch Tuesday and noted the previously mentioned Skype bug.

While the problem was triggered by the high number of restarts, a faulty algorithm caused the network’s self-healing capabilities to fail. Villu Arak, the Skype employee, continued:

… this event revealed a previously unseen software bug within the network resource allocation algorithm which prevented the self-healing function from working quickly. … The issue has now been identified explicitly within Skype.

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