How do third-party tracking cookies work?

Question

I read this question here: How do online advertisers use third-party cookies? about how third-party tracking cookies work, but I'm still very confused. I don’t understand how, if I visit website A (regular website with advertising), how website B (advertising website) can assign my computer an identifier and then find out that I was on website A and others The sites after it have their ads.

Answer 1

First, cookies are set and retrieved via HTTP headers. If your browser sends a request to http://example.com , the response may return with a header that says Set-Cookie: foo=bar . Your browser stores this cookie, and for any subsequent requests from http://example.com, your browser will send foo=bar to the Cookie header. (Or at least until the cookie expires or is deleted.) The browser sends the cookie foo=bar with any request to http://example.com , regardless of who initiated the request or what the context is. If http://example2.com contains the tag <img src="http://example.com/img.jpg"> then the browser will send the cookie foo=bar when it selects http://example.com/img. jpg , although http://example2.com is responsible for the request sent.

So, if website A contains an ad that is served by website B, website B may set a cookie in your browser. For example, website A might use <iframe src="http://websiteB.com/ad.html></iframe> to serve the ad from website B. Then, when your browser goes to http://websiteB.com/ad.html , the response will return with a Set-Cookie header that sets a cookie with some unique random string.If website C also includes an advertisement from website B, then this unique cookie will be sent when the advertisement is on website C will be displayed from website B.

As far as website B knows which actual website you are visiting, there are many ways. In some cases, when the browser sends a request to one website, it tells the website which site you came from. Therefore, when a browser is sent to select http://websiteB.com/ad.html , it may include the HTTP Referer: http://websiteA.com header Referer: http://websiteA.com , which tells website B that the request was initiated by website A. Each time website B sees a unique random string that it has assigned to you, it can check the Referer header to add where you were to its log. If website A is affiliated with website B, A may explicitly indicate B that you are coming from website A. For example, website A may include an advertisement from website B using <iframe src="http://websiteB.com/ad.html?referer=websiteA.com"> and then a link will appear on website B in the query line.

Does it help? Are there certain parts of the answer that you link that do not make sense to you?