The Srbizi botnet is the one that went offline a few weeks ago when McColo went down (see McColo and the Difficulty of Fighting Spam).

Apparently, it recently moved to Estonia but has just been cut off (an impeccable source points me to this article).

Experts say that future botnets will not rely on single servers so much (one term for these future pests is "headless botnets").

Nevertheless, bravo to the ISP community for stopping this one . . . for now.