CNNfn worked with industry leader NetGravity to develop the first policy engine that would allow CNNfn.com to target advertisements based on demographics and other known data points.

Knowledge of the pages visited by a user allows the advertising company to target advertisements to the user's presumed preferences.

So far, however, Google has not used information about the past behavior of searchers to target advertisements, even though the company keeps logs of all searches and its privacy policy allows it to use these for advertising.

Pre-installed software sometimes modifies or replaces the default browser or system settings, in an effort to target specific advertisements to the user; or may otherwise contain functionality the user might consider to be malware.

This strategy, of targeting advertisements at the news media, has been a staple of campaigns ever since.

"Applications, tools, or utilities may use an application program interface to report context data tags such as key words or other information that may be used to target advertisements," says the filing.

The damage it does is more a by-product of its main mission, which is to serve you targeted advertisements or make your browser display certain sites or search results.

WebMD uses this anonymous information to collect general statistics about how people use our site and to target advertisements to your interests and preferences.

It earns money by selling advertising on the website and by e-mailing targeted advertisements to its members.

Personal information has become a valuable asset because many business entrepreneurs are utilizing it to implement targeting advertisements or marketing promotions.