David Cancel, the CTO of the web market research firm Compete Incorporated, raised eyebrows at the Open Data 2007 Conference in New York when he revealed that many Internet service providers sell the clickstream data of their users. Clickstream data includes every web site visited by each user and in which order they were clicked.
Some people are worried about what kind of records search engines like Google hold, but it’s the ISPs we should be worried about by the looks of things. Ridiculous, not two ways about it.
Source: Ars Technica