Who is watching us?

On Habré, there have already been several articles about the “ Do Not Track ” initiative, adopted by major Internet companies, which allows you to indicate that you do not want to be tracked on sites if you enable the DNT option in the browser.
Among the companies supporting this initiative are:

• Facebook
• Twitter
• Linkedin
• Pinterest
• Google
• Yahoo
• Bing

… and many others.
I wondered what the “tracking” looks like in numbers?
We include a healthy share of paranoia and fantasy and count!

Who and why to follow?

First of all, interested in advertising networks, search engines, analytical services, social networks. Having information about the pages you have visited, search queries, characteristics of your client device, your geo-location, sex-age information from social networks, you can make more relevant advertisements, which increases the CTR and, consequently, the profit of advertising networks, is useful for advertisers and more pleasantly for the website visitor. Search engines are beginning to better understand what subject area queries are in, and analytical services are starting to provide demographic data on site visitors, allowing them to more accurately understand their preferences.
It turns out tracking is beneficial to all? Yes, but not everyone likes that services know more about their visits to the Internet than their wife, for example.

And what about the numbers?

Usually, third-party javascript is used for tracking, and that’s what we’ll calculate.
First we get a list of domains that have been visited. To do this, I wrote the simplest extension for Chrome , which gives a list of visited sites (list of domains).
For counting, I made a service on my knee (php + twig + mongodb + twitter bootstrap) for a couple of evenings that runs through the list of sites given to him and determines on which sites which third-party javascripts are connected.
My result - I’m followed up on 126 of 174 sites .
As a result, only third-party scripts are taken into account, because their own tracking systems of large portals are not taken into account. A fairly simple search for connecting javascripts is also used, because obfuscated connections are also not taken into account.

How to protect against tracking

1. Declarative methods when you simply declare that you do not want to be followed, for example, DNT or the privacy settings of individual services. They run into the question of trust and honest name of the tracking companies.
2. Active methods - incognito mode on websites, use of extensions like AdBlock , Ghostery , periodic cleaning of cookies, absence in social networks.
This works, but it will reduce the income of webmasters on whose sites will not show you advertising, or will decrease the relevance and CTR of the displayed ads. Don't you feel sorry for them?