How do websites track you?
When you load a typical web page, you are not just talking to that one website. The page quietly pulls in scripts, images and ads from a dozen or more other companies, and many of them are there to learn about you.
Each of those companies only sees a little on any single site. But because the same few trackers sit on thousands of sites, they can stitch your visits together into a surprisingly detailed picture of your interests.
Here are the main tricks they use, and which of them your browser can actually stop.
This is roughly what happens when you open one article. Your browser contacts the site you asked for, and several companies you did not. Tap the laptop to see what a tracker blocker changes.
How websites track you
The four main tricks
Third-party cookies
An ad network drops a cookie with a unique ID the first time one of its ads loads in your browser. Every other site that runs its ads sends that same cookie back, so the network can line your visits up into one long history.
On a news site
Later, on a shoe shop
Tracking pixels
A tracking pixel is an invisible image, often a single see-through dot, loaded from a tracker's server. Simply loading it tells the tracker that you opened the page or email, when you did it, and your IP address.
Browser fingerprinting
Even without cookies, your browser gives away a lot about itself: screen size, time zone, language, fonts and graphics chip. Put together, those details are often unique enough to recognise you again, and clearing your cookies does not change any of them.
Being signed in
When you are signed in to a big platform, its buttons and scripts on other sites can tie what you do there to your real account. There is no guessing involved, because your login cookie travels with every one of those requests.
One profile, built from many small visits
No single site learns much. The value is in joining the dots, and the companies that sit on the most sites end up with the most complete picture.
What helps, and what does not help much
This helps
- Blocking third-party cookies in your browser settings
- A content blocker that stops known trackers
- Browsers with tracking protection built in, like Firefox, Safari and Brave
- Signing out of big platforms when you are not using them
This does not help much
- Incognito mode on its own
- Clearing cookies, if you are being fingerprinted
- A VPN, against trackers that rely on cookies or logins
Most tracking is not done by the site you are reading but by the handful of companies it invites onto the page. Cookies, pixels, fingerprints and logins each give them a piece of the puzzle. You cannot stop all of it, but blocking third-party cookies and known trackers takes away the biggest pieces with very little effort.
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