It turns out that it was Microsoft that brought down Skype for two days earlier this month. Microsoft's monthly software update (known as Patch Tuesday) triggered millions of computers to reboot at the same time, which always puts an unusual strain on major Internet companies such as Skype.
As Alex from RiskManagement Insight points out, this is equivalent to a form of DDOS (distributed denial of service) attack. From a risk management perspective, it may not matter very much whether an attack is deliberate and malicious, or merely an accidental side-effect of some entirely innocent action.
Although Skype had survived previous Patch Tuesdays without incident, it seems that this month's Patch Tuesday triggered a previously unknown bug in Skype's software. As Alex points out, it is practically impossible to construct a test environment large and complex enough to simulate this scenario.
I haven't seen any figures, but I have little doubt that Skype's competitors (including Microsoft) must have experienced an unusually high level of new registrations during Skype's misfortune. Now that we have become accustomed to free voice calls over the Internet, it seemed outrageous to return to the almost mediaeval practice of paying real money for talking over the telephone, so my colleagues and I signed up to Yahoo Messenger.
It's an ill wind ...