An anonymous reader points out a story in the Washington Post, which begins:
"A single response from 12 million e-mails is all it takes for spammers to turn annual profits of millions of dollars promoting knockoff pharmaceuticals, according to an unprecedented new study on the economics of spam. Over a period of about a month in the Spring of 2008, researchers at the University of California, San Diego and UC Berkeley sought to measure the conversion rate of spam by quietly infiltrating the Storm worm botnet, a vast collection of compromised computers once responsible for sending an estimated 20 percent of all spam."
The academic paper
(PDF) is also available. We've previously discussed another group of researchers who were able to infiltrate the botnet
for a different purpose.