There are two main points to take away from the Kelihos.B takedown. The first is that malware writers, as smart as they are, are really dumb.
Forget about malware for a moment, and imagine the architecture involved in Kelihos.B was part of a legitimate distributed-computing business system. Would you invest all that time and effort to build a P2P network and design a mechanism for message propagation, then leave it wide open to attack by failing to include any form of authentication mechanism? It’s complete lunacy. If you did it in a commercial environment, you’d get fired. Out of a cannon. Into the sun.
The second interesting point is that this botnet exclusively infected OS X, which is a pretty big shift in focus from the previous major botnets like Conficker and Mariposa. I’m actually surprise it took this long for a major OS X botnet to surface, considering the general stereotype of Apple users. They’re usually not tech-savvy, generally more wealthy than the average Windows user, and often under the illusion that “there are no viruses for Macs!”. The perfect storm of getting pwned.
I have a feeling it won’t be very many years before the distribution of malware across Windows and OS X ends up being close to equal.