A two-day outage that left millions of Skype users unable to use the popular Internet phone call program was caused by an abnormally high number of restarts after a routine software update, the company said Monday. The worldwide outage, which began on Thursday and ended on Saturday, left millions of Skype users unable to log on to make phone calls or send instant messages.

Luxembourg-based Skype, part of online auction giant eBay Inc, has more than 220 million users in total but typically has 5 million to 6 million users online at any given time. In January, Skype reported that it had counted 9 million users online at one time.

In an update to users on Skype’s Heartbeat blog, employee Villu Arak said the disruption was not because of hackers or any other malicious activity.

“The disruption was initiated by a massive restart of our users’ computers across the globe within a very short timeframe as they re-booted after receiving a routine software update,” he wrote in the message, which was posted at 0535 GMT.

“The abnormally 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,” he said in the posting.

The outage was a critical moment for the company, founded in 2003 by Niklas Zennstrom and Janus Friis, and was the first major outage since October 2005 when its service was down only for a few hours.

“This disruption was unprecedented in terms of its impact and scope,” Arak wrote. “We would like to point out that very few technologies or communications networks today are guaranteed to operate without interruptions.” - AP

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