- <p>Third-party cookies are set by portions of a website that are loaded from servers different from the URL at the top of the page.
- For example, most website that have advertisements load them from a third-party ad broker, like Google’s
- <a href="https://www.google.com/adsense/start/#?modal_active=none">Ad Sense</a>. Every time the website loads, it requests the ad
- broker to display an ad. The ad broker analyzes any information they may have about the user, looks at the current
- rate advertisers are willing to pay for their ads, and selects the one to display. The section of the website that displays
- the ads is loaded from the third-party broker’s server instead of the main server.</p>
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- <p>Because most of the advertisements on the internet are processed by only a few brokers, it didn’t take long for them to realize
- that they could set a tracking cookie on the user’s device and know every place that user goes. Every time an ad loads from a broker,
- the first thing it does it check to see if if the device already has a unique serial number in a tracking cookie. If it does, it looks up
- the profile for that serial number and makes a note of the new site. This is why a user can do a search on one website for a
- product they typically don’t look for, like walnuts, and then suddenly start seeing advertisements for walnuts on every
- website they visit.</p>