How to track users across domains?

Question

We got this idea yesterday. User visits our site and is marked. Then, when they visit other sites, such as CNN, they are aimed at adding to our site. Therefore, when they are exposed to us, they begin to see us everywhere, creating the illusion that we are more than us.

The person writing said that this was done using cookies. I was very skeptical, as I do not believe that it is all the same to find out which cookies are selected for another domain. So I wanted to try to figure out how this was done. The seller called this technology pixel tracking.

I have never heard of pixel tracking, but from my research I found that it places 1 pixel image that refers to a script in another domain with parameters that must be executed. My first thought was, OK, maybe this is possible. But I still do not know how?

Can someone explain how they can mark you as having visited our site and then see this tag on another site? Is this from your IP?

Answer 1

At the bottom of the site (CNN) in this case is the img tag, for example:

<img src="http://www.webmarketingCompany.com/pixel.php?ID=623489593479"> 

When a user visits the website (CNN) and the browser displays the page, he also sends http requests for all images, including the http://www.webmarketingCompany.com request for the pixel.php image, which includes the identifier as the get parameter. pixel.php not only returns an image, usually a transparent gif 1x1 (therefore, it does not appear on the displayed page), but can perform a number of additional processing using the ID value; and he also has access to any cookies webmarketingCompany.com, which are also sent with an http request.

Of course, CNN should agree to include the img tag in its html. It is usually used as a tracker by third-party marketing companies working on behalf of CNN to determine who visits their site, which pages they view, etc.

But since this is a PHP script, it can perform a number of additional functions, such as setting additional cookies. If webmarketingCompany.com also processes commercials on behalf of CNN, they can make creative choices for the ads they prefer to serve.

Such cross-client pollination is disapproving, of course, here in the UK.

Answer 2

What you describe is pretty standard across all ad networks. The only difference here is that they will place this cookie on your site.

As long as the browser "accepts third-party cookies" is set to true, this will work as the seller said. Most browsers are set to true by default, the only exception I can think of is Safari.