Skype has fixed a software bug that made the internet telephony service almost unusable for two days last week.
According to a statement released by Skype on Monday, the outage — which affected the majority of Skype's user base — came about on Thursday with "a massive restart of our users' computers across the globe within a very short timeframe".
The restart came about as the result of a routine Windows update. "This caused a flood of login requests which, combined with the lack of peer-to-peer network resources, prompted a chain reaction that had a critical impact," Skype's statement said.
The VoIP company, which is owned by eBay, admitted that the majority of its users had been unable to access the service between Thursday and Saturday.
A spokesperson for the company confirmed to ZDNet.co.uk on Monday morning that a fix was now in place for a bug in Skype's network resource allocation algorithm. The bug, revealed for the first time on Thursday, had stopped Skype's in-built "self-healing function" from working properly, causing the most severe outage in the history of the popular VoIP client.
Skype was keen to say that the outage was not the work of hackers or any other malicious activity, and it claimed that its users' security "was not, at any point, at risk".
"This disruption was unprecedented in terms of its impact and scope," the statement said. "We would like to point out that very few technologies or communications networks today are guaranteed to operate without interruptions. We are very proud that over the four years of its operation, Skype has provided a technically resilient communications tool to millions of people worldwide."
Mark Main, a broadband analyst at Ovum, blogged on Friday that it was "quite an achievement" for Skype, now almost four years old, to have gone so long without an outage of this severity. However, he also suggested that Skype's quality of service had been deteriorating recently, and he said that resilience remained a common issue for commercial VoIP services.
"Perhaps we should still consider some VoIP services as being like a shortcut over rocky ground instead of the smoother, but longer and well-trodden path," wrote Main. "Many users may not yet have decided how many jarred ankles they will tolerate over that rocky ground. You still broadly get what you pay for in telecoms and there is a compromise users must accept in these relatively early days of VoIP-based voice services, especially with the free on-net services."
Thirty percent of Skype's 220 million customers are business users, according to the company's own figures, with the vast majority of those choosing internet telephony to save costs.