InternetPrivacyUncategorizedWeb Browsers

Wait – HOW MANY websites are tracking me?

Collusion graph
Collusion graph

If you’ve ever wondered how a certain website ad seems to know who you are, even though you haven’t logged in to it, wonder no longer. The Mozilla Foundation has an add-on for their Firefox web browser called Collusion. What does Collusion do? It shows the relationships between all of the websites you visit.

Have you ever wondered how ads on websites seem to know a lot about you, even before you log in to them? The method used is is known as “tracking cookies.” Cookies are bits of information, mostly harmless, that your web browser allows a website to store on your computer. This lets the website know who you are when you return. For instance, if you’ve ever gone to any number of websites, e.g. Amazon, eBay,¬†Facebook, Gmail, UPS, and had them welcome you back by name, this is done through a cookie. When you log in to that site, it makes a note of who you are. The next time you return to the same time, it asks your web browser for its cookie back, and if it recognizes the cookie, it knows who you are. This is not only mostly harmless, it’s also pretty useful!

However, cookies can be used for evil as well as good. This is usually done in the part of “third party cookies.” Wikipedia defines third-party cookies as follows:

First-party cookies are cookies set with the same domain (or its subdomain) as your browser’s address bar. Third-party cookies are cookies set with domains different from the one shown on the address bar. The web pages on the first domain may feature content from a third-party domain, e.g. a banner advert run by Privacy setting options in most modern browsers allow you to block third-party tracking cookies.

As an example, suppose a user visits, which includes an advert which sets a cookie with the domain When the user later visits, another advert can set another cookie with the domain Eventually, both of these cookies will be sent to the advertiser when loading their ads or visiting their website. The advertiser can then use these cookies to build up a browsing history of the user across all the websites this advertiser has footprints on.

By doing this, advertising networks allow two unrelated sites to collect and share information about you, allowing them to aggregate more information about you than they could independently.

Collusion illustrates this relationship beautifully, to demonstrate to the user just how many websites are talking about you behind your back.

To take Collusion for a spin, try the following:

  1. If you have not already, download and install Firefox.
  2. Once you have it installed, open it, and then download and install Collusion.
  3. Close down all windows in your Firefox browser, then start it up again.
  4. Under the Tools menu, click “Collusion Graph.” This will open a new tab showing the relationship between websites you are on. It should start out with almost nothing.
  5. In another window, start visiting a few websites that you frequent. Just browse the web for 5-10 minutes, hitting sites you normally visit.
  6. Go back to the Collusion graph, and see which sites are talking about you behind your back.

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