David Cancel, CTO of web market research firm Compete Incorporated, claimed at the Open Data 2007 conference that many ISPs sell the clickstream data of their users. This includes every websites you visit and the order in which they were clicked.
The data is not sold with accompanying user name or information, but merely as a numerical user value. However, it is still theoretically possible to tie this information to a specific ISP account. Cancel told Ars that his company licenses the data from ISPs for millions of dollars. He did not give a specific figure about what this broke down to in terms of dollars per ISP user, although someone in the audience estimated that it was in the range of 40¢ per user per month—this estimate was erroneously attributed to Cancel himself in some reports on the event. Cancel said that this clickstream data is "much more comprehensive" than data that is normally gleaned through analyzing search queries.
The revelation brings to mind the minor scandal that erupted when AOL was found to be giving away its search results to researchers—this was discovered only after a large sample of data was accidentally released to the public. Clickstream data is, as Cancel admitted, much more interesting to marketers than search engine data.
There is some evidence that the data traditionally gathered by market research firms such as Compete may not be as accurate as the companies had hoped. Establishing "ISP relationships" helps to augment that data—traditionally gathered by user-installed toolbars—but may not be, strictly speaking, an ethical practice.