According to this Washington Post article, the bulk of the downloading pertained to some 913 titles, each of which was illegally downloaded about 10,000 times:
The study, conducted by the online monitoring and enforcement service Attributor, highlights the drain from piracy on publishers revenues and the need for more effective protections online for copy-righted material.[...]
The study examined 14 categories to capture a representative sample of the industry, including business and investing, health, mind and body, fiction and reference. Business and investing titles suffered the highest number of illegal downloads, averaging 13,000 copies per title, with a potential loss of more than $1 million on each title, Attributor estimated. Popular fiction titles averaged about 6,000 illegal downloads each.I have also linked to the study so that you can see the details for yourselves, including a listing of the sites responsible for allowing the bulk of the 9 million illegal downloads. I'm going to visit some of those sites (if the links are real) just to see what's going on. I suspect that the industry is watching them closely, too, and I wonder how much increased traffic the sites will receive now that they've been "outed." This is one of those Catch-22 situations for publishers.
"Freakonomics" by Steven Levitt and Stephen Dubner, for example, was pirated 1,132 times from just one of the hosting sites. Attributor would not release total individual numbers. In fiction, "Angels and Demons" by Dan Brown was pirated 8,177 times from one site.