"As major botnet operators have moved from top-down C&C infrastructures, like those employed throughout the 1990s and most of the last decade, to more

http://it.slashdot.org/story/10/06/07/2335210/Botnets-Using-Ubiquity-For-Security?art_pos=12

"As major botnet operators have moved from top-down C&C infrastructures, like those employed throughout the 1990s and most of the last decade, to more flexible peer-to-peer designs, they also have found it much easier to keep their networks up and running once they're discovered.