Ezhenito noted some research pointing out the (maybe) surprising bit of research that 6 botnets are responsible for 85 percent of the world's spam. That seems a bit high to me, but the only aspect of spam I am an expert in is *getting* it.
"The Avis WIZARD decides if you get to drive a car. Your head won't touch the pillow of a Sheraton unless their computer says it's okay." -- Arthur Miller