Surveillance 2: All for one and one for all

As recently as five years ago, putting all those pieces of data together was too cumbersome and expensive a task for anyone but the larger credit-reporting agencies and pricey private detectives. Today, however, it's incredibly easy for even the smallest business to convince you to give up small bits of information, then gather them together to form a complete profile. Critics call this process "data creeping".

Not surprisingly, Internet advertising agencies are the most effective when it comes to recording your movements in cyberspace -- usually without your knowledge. Here's how the process works:

You visit a Web site that contains a banner ad from a major Internet ad agency. Without your knowledge, your browser connects to the ad agency's server, which then plants a cookie on your computer that contains a 32-digit ID code. Each time you visit a new Web site that contains ads from the agency, the cookie sends your unique ID code back to the agency's server and records your movements -- helping to build a detailed trail of which Web pages you visit. And if at any time you fill out an entry form, you inadvertently supply your email address.

Congratulations! You've just supplied the missing link to help that ad agency assemble your entire dossier into one neat package. Without any personal details, the agency can still use your ID to determine which banner ads it displays -- and it always chooses the ads you're most likely to respond to. And once it's got your email address, the agency can cross-reference your name, address and other personal details from other databases. If the ad agency can convince you to supply any more details, it can add you to highly targeted junk mail lists and even sell your profile to third parties.

Take me to the Surveillance 2 ZDNet News special.