As more users install ad blocking software and browsers such as Firefox and Safari start blocking some ad trackers by default, advertisers decided to come up with a new solution to track everything you do.
This new technique is a bit technical, but I will try to keep it high level.
Typically, the company tracking you is a separate company from the company who’s website you are visiting because not only do people want to know what you are doing on their website, but also what you are doing on every other website in the world. This logic is what created the third party ad tracking business.
But browsers can tell, if you are visiting ABC.COM, if that web page makes a request for some data from XYZ.COM – a third party.
Those requests come in many forms. It could directly load data from or save data to that third party.
Or it could save a “cookie” from that third party with information associated with the site you are visiting so the ad tracking company can track you everywhere.
As people have become smart to this and taken anti-tracking measures, advertisers tried Adobe Flash cookies. That didn’t work well because many people (like me) think Flash is insecure and even Adobe is killing it in December 2020.
So the ad trackers came up with a new idea.
If ABC.COM wants to track you, the ad tracking company asks ABC to create a new subdomain, say trackyou.abc.com and point that subdomain to the tracking service. Since the core part of trackyou.abc.com is still abc.com, it doesn’t look to the browser like there are any third parties. But since the tracking company runs trackyou.abc.com, they can collect whatever data they want.
It turns out that it is possible, with some work, to block this if you use Firefox, but not with any other browser. Most browser makers are in the business of selling your data, so they are a bit conflicted.
In fact, a Google search provides lots of articles on how to do this yourself.
Advertisers are just trying to make a buck, not do you in (mostly). Source: The Register