When a person views a product on a retail Web site, the user’s browser submits information about what he is looking at to third-party advertising networks, such as doubleclick.net.

The information is stored in a
browser cookie — a small piece of code that lets ad networks and sites share information on what visitors view or buy. Users can clear these cookies periodically to clear out their record with ad networks.

If that person later clicks on
another site in the same advertising network, ads for the product the user viewed at the first retail site could show up. The ad is targeted to the user in hopes of drawing him back to purchase the product.

  • Cookies, or user data, shared by one advertising network
  • Other cookies store user preferences and authentication codes
Product
An advertising
network
Product ad
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SOURCE: Network Advertising Initiative, Digital Advertising Alliance, Facebook, Google.