The blogsphere is abuzz with reaction to Skype's second attempt to explain what caused the recent crash of their entire "peer-to-peer" network, but I haven't seen any comment on the one thing that struck me (in their 4th paragraph):
Once we found the algorithmic fix to ensure continued operation in the face of high numbers of client reboots, the efforts focused squarely on stabilising the P2P core. The fix means that we’ve tuned Skype’s P2P core so that it can cope with simultaneous P2P network load and core size changes similar to those that occurred on August 16.
As I commented earlier, we know from presentations by Desclaux & Kortchinsky at Blackhat Europe (PDF) in March 2006 and at Recon in June 2006 (PDF in 2 files: one and two), that there is substantial traffic between the (3rd-party-owned, distributed, P2P) supernodes that form the core of the Skype P2P network and Skype's (centralized) login servers.
If Skype's explanation is correct, it's clear Skype also has a way of distributing parameters to supernodes that tune their behavior. I'm not surprised. It's a logical to design in both measurement and tuning capabilities.
But such centralized capabilities also represent a potential venerability. What would happen if a black hat got access to those tuning capabilities...