In a Wednesday, Lars Rabbe, Skype's chief information officer, provided more details on the outage that kept the instant message, Internet telephone and video chat service offline for much of Dec. 22 and parts of Dec. 23.

Previously, Skype had , the term for systems running Skype that also act as directories, for the outage.

Today, Rabbe said a bug in an older version of the Windows Skype client was at the root of the service's failure, although the flaw did not trigger the blackout.

The bug in version 5.0.0152 caused those Windows clients to crash when they received a delayed response from "a cluster of support servers responsible for offline instant messaging" that had been overloaded, Rabbe said. About 50% of all Skype users were running the buggy 5.0.0152 version of the Windows client last week.

Rabbe did not explain how or why those servers -- which triggered the Windows client crashes, and thus, the outage -- became unresponsive last Wednesday. Skype did not respond to questions today about that initial server overload.