Subscribe to one of our news e-mail lists . There's a quick and easy way to find out a little about how much is known about you. You and a friend, using separate computers, go to the same Web page and compare the ads on that page. That is evidence that their computers have been linked to certain products because sites they visited in the past had codes buried in Web pages to track them.
Web bugs can also alert the sender when a viewer has opened an e-mail ad.
A company known as Engage is one of about a dozen Web advertising firms that represents hundreds of sites and creates a personality profile based on where you browse. At Engage, it's company policy not to associate a name or face with a cookie or a ping. Other companies, however, make it their business to find out precisely who you are. If you register with a number of different ad companies, perhaps for a contest, and there are a number of different contest sites, then an ad network can watch where you go on the Web and match that information with your identity. Opportunities for exploitation' And in an industry where technology moves faster than regulations, that trend can result in an invasion of privacy.