Botnets in general are nothing new, in fact are very common now. For a good description: Botnet From Wikipedia
This is why it is imperative to keep your Windows updated and install and maintain basic security programs as recommended here:
Simple and easy ways to keep your computer safe and secure on the Internet
From the numbers you've cited, it sounds like you're talking about one specific malware. It would be nice to see a link to the information you ran across so we could be better able to comment on it. It can get confusing because the name of any malware in question often depends on which security vendor or other entity is describing it. But in general, you can tell some infections that are botnets as they have Bot
in their name, such as Agobot
, etc. There are others without bot in the name, and yes, it is fairly scary as they can configure themsleves and basically each infecion is different to each infected machine, which makes it hard for AV vendors to keep up with definitions to find and remove all the elements.
Basically this is a big reason you see so many HijackThis logs, both here and in other forums.