It's a good thing Microsoft is so hot to pursue and crush the invation of botnets (by charging and quarantining its customers, as well as prosecuting bad guys, though none of those methods are getting any easier, though Computerworld blogger SJVN has a rundown of the best methods ).
The report -- actually a series of global-infection-rate listings that, oddly, are in XPS or PDF format, not XLS or anything Webby and active so you can change the order you view them and learn what you want about the data rather than learning what's presented alphabetically -- also has lots of info on what they're after, the leading botnet families , updates on famous botnet virii, how to detect and fight them, and all kinds of other good background, mostly arranged and connected in slightly clunky ways that will annoy you and make it harder to find answers to your specific questions -- this is Microsoft, it's a family trait.
Perpaps most useful (and most straightforwardly written) is the Managing Risk section that offers advice on Protecting your organization, your software and your people notice where humans fall in that hierarchy).
The site would be a perfect primer, update and guide on malware and botnets, if there were more links to deeper information (much of it is a little basic), and the engine under the Search bar were something that brought up answers more quickly and precisely than the largely-useless Bing.
On the other hand, in this article, CISO's Bill Brenner gives a very clear explanation of why botnets keep growing and it's getting harder to fight them.