Skype denies failure was due to DoS attack

Experts have raised questions about the resilience of voice-over-IP (VoIP) provider Skype in the aftermath of last week's major service failure.

The company, owned by internet auction giant eBay, resolved last week's major outage over the weekend, but the loss of service has prompted questions about the reliability of it and other such services.

An update posted today to the Skype status page said the problem was caused when users rebooted their systems after downloading a routine service update.

Skype spokesman Villu Arak said the unusually high number of restarts and subsequent login requests, coupled with a lack of peer-to-peer network resources, revealed a previously unseen software bug within the network resource allocation algorithm.

This bug prevented the network's self-healing function from working quickly, rendering services unusable for more than 48 hours until it was resolved and normal service resumed on Saturday.

Arak was quick to dispel rumours that the outage had been caused by a denial-of-service (DoS) attack, saying: "We can confirm categorically that no malicious activities were attributed or that our users' security was not, at any point, at risk."

He also defended the provider's track record, adding the disruption was "unprecedented in terms of its impact and scope".

Mark Main, senior analyst with research firm Ovum agreed that Skype had a relatively good track record in terms of service reliability up until now. But last week's outage served to highlight some growing concerns about the service.

"There have been a few signs in recent months that possibly all is not well with Skype. Numerous people have remarked to me that 'Skype is getting worse,'" he said.

He stressed that there is still a danger that services designed to be highly disruptive to traditional telecoms business models have been developed without sufficient regard for resilience, adding that similar outages would only see users migrate to alternative service providers in what was already a crowded market.

Main said: "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 the free on-net services."

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