eBay’s explanation for last week’s failure of its Skype communication service has left many users still wondering what caused the worst outage in Skype’s five-year history.

Millions of Skype users were knocked offline last week when a programming bug made it impossible for most users to connect during a 36-hour period, starting last Thursday.

On Monday, Skype said the disruption was kicked off when a large number of Skype users restarted their computers after installing Microsoft’s monthly security software updates, which were pushed out to Windows users starting on Tuesday.