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Date: Tue, 21 Aug 2007 04:52:23 +0300
From: "Valery Marchuk" <>
To: "Steven M. Christey" <>,
Subject: Re: Skype Network Remote DoS Exploit

Skype made a funny "explanation" of the problem...

Lets say, people download updates on Tuesday in the US, on Wednesday in 
Europe and just happen to reboot their computers simultaneously on Thursday? 

As I remember, there were two primary theories of the problem source:

  1.. Microsoft's updates
  2.. DoS attack
It seems Skype has decided to make their own theory based on these two: so 
it was a DoS, but not an attack, and it was updates fault, but not Microsoft's.

I do believe that the DoS Exploit, published at, might 
have such an impact, but it's impossible to prove anything and it's not 
necessary. I just would like to say, that Skype could came up with more 
realistic story, for example: someone made a mistake in the code, or they 
were trying to implement new feature and everyone would believe, even me :)

Best regards,

Valery Marchuk

----- Original Message ----- 
From: "Steven M. Christey" <>
To: <>; <>
Sent: Monday, August 20, 2007 8:39 PM
Subject: Re: Skype Network Remote DoS Exploit

> The outage being experienced by Skype was apparently due to massive
> simultaneous reboots and reconnects after systems installed their
> Windows patches.
> from
>   The disruption was triggered by a massive restart of our users'
>   computers across the globe within a very short timeframe as they
>   re-booted after receiving a routine set of patches through Windows
>   Update.
>   The high number of restarts affected Skype's network resources.
>   This caused a flood of log-in requests, which, combined with the
>   lack of peer-to-peer network resources, prompted a chain reaction
>   that had a critical impact.
> I wonder how many other services are impacted by simultaneous Windows
> scheduled updates.
> Anyway... given that this was going on at the time the
> exploit was released, and the exploit only claims a DoS (and only
> seems to make a series of requests to long URIs), was the exploit
> actually effective, or was the "DoS" just part of the larger outage?
> - Steve 

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