After a two-day outage that left millions of Skype users unable to sign-in to the service, the eBay-owned company on Sunday announced its service was back to normal. According to the company, the failure happened after a massive restart of its users' computers across the globe triggered by a routine set of patches through Windows Update.

Although the Skype network has a built-in self-healing function, a design error prevented the function from working as expected:

"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" Skype employee Villu Arak said. "This event revealed a previously unseen software bug within the network resource allocation algorithm which prevented the self-healing function from working quickly" he added.
Although the company stressed that no malicious activities were involved in the outage, it provided no details on why previous Windows upgrades have not caused similar problems, or whether future upgrades could set off another network outage.

As businesses continue to target cost savings, Skype and other PC-based voice over IP application have become increasingly popular. However, they still aren't seen as reliable or convenient to use as a traditional landline phone or a cell phone.