VoIP provider Skype has claimed that the outage that crippled its service last week was down to a surge of users logging on after installing Microsoft's latest security update.

The crash caused a two-day outage of the service and prompted speculation that the VoIP provider had fallen victim to a denial-of-service attack.

Skype spokesman Villu Arak said in a posting to a company blog that, while the problem was caused by a system crash, it was not due to a deliberate malicious effort.

Arak explained that the outage arose when a large number of users installed Microsoft's August security update.

After restarting their computers the users all attempted to log in to the Skype service, causing an overload on the components of the service that handle peer-to-peer connections.

A "self-healing" feature would normally intervene and allow the system to correct or compensate for the increased load. But the feature failed to activate and the result was a chain reaction that took down the entire service.

"The issue has now been identified explicitly within Skype," Arak declared. "We can confirm categorically that no malicious activities were attributed and that our users' security was not, at any point, at risk."

Arak said that Skype has already patched the code responsible for the crash.

He did not say that the system would be able to weather a similar flood of traffic in the future, but did pledge that users would not be "similarly effected" the next time the issue arises.