"The targeted Internet advertising phenomenon is viewed with growing concern by privacy advocates who fear that controversial practices like behavioral tracking are ripe for abuse. A coalition of consumer and Internet rights groups have written a joint open letter addressed to the House Committee on Energy and Commerce in which they articulate some specific concerns about behavioral tracking and provide an outline of proposed regulatory guidelines that they believe should be enforced to protect consumers.
Behavioral tracking, a practice that is used by all of the major Internet advertising networks, involves building a profile of information about users based on which websites they visit. This information helps ad companies display advertisements that are more narrowly targeted to the interests of individual users. Major consolidation in the Internet advertising industry has made it possible for a small handful of very large advertising companies to broadly track user behavior across the entire Internet." – Content courtesy of Privacy advocates want regulation of behavioral advertising – Ars Technica