How Do Internet Advertisers Use Third-Party Cookies?

Question

If a given web server can only read cookies from those set within its own domain, how do Internet advertisers track user\'s web traffic from websites outside of their networ

Answer 1

Companies like Facebook, Google and Doubleclick's business models work because much of the Internet community voluntarily hosts a Javascript file for them. I assume that 90%+ of large websites all use Google Analytics or run Google ads. And they all used Doubleclick ten years ago. The actual cookie is probably just a simple user id. That's enough information to update your anonymous profile.