When I was looking for more information about botnets I stumbled over a fun presentation on "Life, Love and War in the Underground". It is from late 2003 but I think the basic facts are still valid. According to the findings of the Author Rob Thomas there exists a livid marketplace in the IT underground. Botnets, 0days and rootshells are swapped or sold for hard currency (e.g. a new exploit sells for about $100 to $500). But to participate you have to know how to speak 1337...