At the Open Data 2007 Conference in New York, David Cancel, the CTO of the web market research firm Compete Incorporated, revealed that many Internet service providers make millions by selling the clickstream data, meaning every web site visited by each user and in which order they were clicked, of their users. 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 said that this clickstream data is "much more comprehensive" than data that is normally gleaned through analyzing search queries.
Most tech-savvy users are aware that the Internet isn't exactly privacy heaven. Everything can be tracked. Nonetheless, ISPs that expect to profit from this data should at the very least inform their users that they are doing so. Some US Congressmen are calling for new laws to be enacted to protect the privacy of Internet users. For his part, David Cancel says he "strongly supports an increase in the methods and degree to which disclosure is communicated," not only for clickstream data but for any kind of data collected on users' personal surfing habits. He stated that "all users should be informed explicitly when their data can be sold to a third party."
News source: Ars Technica