What is a tracker?

A tracker is a small piece of software, embedded in a website, that records your activity on the site. Trackers send information about the activity they’ve recorded to a tracking server, owned by the company that made the tracker. Web ads usually include trackers, though you couldn’t tell just by looking at an ad. Social media buttons on other sites (such as “Like” buttons) also include trackers. Most trackers are invisible.

How do trackers work?

Trackers record your browsing activity and send it to a server and—most importantly—try to recognize the same person as they browse different websites. Correlating your activity across many different parts of the Web creates a more detailed profile of you for ad targeting.

Trackers use two main technologies to recognize Web users: cookies and fingerprinting. A cookie is a small piece of data stored in your browser. The tracker stores a unique string of characters in a cookie and reads it back any time your browser goes to a site that includes the same tracker. Fingerprinting combines a variety of characteristics of your browser and device (such as your browser and OS versions, your screen size, and many others) to recognize you.

Why are trackers used?

Trackers build data profiles of people, which can then be used in targeting ads. The more detailed the profile—especially about things like spending habits and income level—the better targeted the ad.

Targeted ads are more likely to result in “conversions” (sales), so advertisers are willing to pay more to place ads with better targeting. That makes the ads more lucrative for the sites that show them, and the ad networks that serve them. All the financial incentives push towards more and more invasive online surveillance. On the modern Web, privacy is disincentivized.

What activity do trackers record?

The most basic information they record is which pages you visit, and how long you stay on each page. They also record what you search for and the links you click. On e-commerce sites, they’ll record what you buy. When the tracker sends data to its server, the server can see your IP address, which can even reveal your physical location.

All of this data can be correlated with personal information that you’ve given to websites voluntarily, such as your name and email address. As you can see, trackers can build a surprisingly complex—and complete—profile of you: where you are, what you like, even who you are.

What are the privacy concerns with trackers?

Trackers gather data about your online activity, and that data ends up in the hands of companies you have no relationship with, and that you’ve probably never heard of. These ad tech companies can collect your data without your informed consent, and they have no real incentive to keep your data safe. Ad tech can then use your data to make money, often by reselling it to yet more companies you have no relationship with.

These profiles of you can be correlated across many different data sources, and even with public data sources like real estate records. You have no control over any of this, and you likely won’t know it’s happening. And if you don’t know it’s happening, you have no control over what data is collected or how it’s stored, exposing you to hacking and data breaches.

How can I avoid trackers?

The best option is to use a browser, like Brave, with built-in tracker blocking. Brave blocks ads and trackers by default, as well as third-party cookies and a variety of fingerprinting techniques. This blocking impedes a tracker’s ability to recognize you as you browse different sites.

Another way to avoid trackers is to use an ad-blocking extension on your browser. Ad-blocking extensions can block both ads and the trackers embedded in them, using lists of known tracking servers (a filter list) to prevent the browser from loading trackers from those servers, or sending any data to them. However, extensions present their own privacy and performance risks—they still require a leap of faith.

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