Internet advertisers and third-party cookies - clarifications?

Question

I read this question about how the third cookie is set, which I already know about:

There are three ways to do this:

• Script ( application/javascript ) type mime (which is created on the server side), which can also set cookies. (along with script response).

• img link <IMG href="http://www.advertiser.exmaple/add.cgi?source=example.com&user=1032354">

• submit form in iframe (for safari)

Also, this answer explains it pretty well.

Question:

I clicked on the glasses element in example.com .

How does advertiser.com know that it should show me ads for glasses ? img / script / form submission to an iframe is executed (with query string value for glasses ) for each click on example.com? (I hardly believe)

(even if this is the case, it means that both advertiser.com and example.com must agree that item #447 is glasses .... they both share db? --- huh?)

How it works?

Answer 1

When you visit http://www.example.com/glasses , resources downloaded from this page (images, scripts, etc.) are requested using the Referer: http://www.example.com/glasses HTTP- heading. In this way, the advertiser knows which page you are on. Of course, they can parse the URL for keywords or make a request and parse HTML code, but more often they already know everything they need. They know that example.com uses their ads, so they often browse the website using a sitemap.

If the Referer header is not sent (everyone can disable it in their browser), the advertiser can get the URL using JavaScript, which can send cross-origin requests in a variety of ways, including CORS. The script can also instantly get the right keywords by parsing the current HTML of the page.

With keywords, the advertiser’s software will determine which ads you should see. And by the way, they will create your profile in their database and set you a cookie with your ID to track your preferences and behavior - and show you more personalized ads in the future.