Key Takeaways
- Cookies are small files stored in your browser that let sites remember you across visits.
- Third-party trackers follow you across many different websites, not just the one you are on.
- Browser fingerprinting identifies your device without storing anything, making it harder to block.
- No single privacy tool stops all tracking methods at once.
- Adjusting browser settings and using tracker-blocking tools reduces exposure meaningfully.
Web tracking
Web tracking is the practice of collecting data about a person's online behavior as they visit websites and use apps. Trackers record what pages you view, how long you stay, what you click, and sometimes where you go next. This data is used to build profiles that advertisers and other third parties can draw on. Tracking happens through several different technical methods, and most operate without any visible sign to the user.
Tracking can occur at the network level (via IP address logging), the browser level (cookies, local storage), and the device level (browser fingerprinting). Each method has different persistence and different defenses.
How cookies work and what they actually store
A cookie is a small text file that a website saves in your browser when you visit. It contains a unique identifier so the site can recognize you when you return. Without cookies, a shopping cart would empty itself the moment you navigated to a new page, and you would have to log in again on every click.
First-party cookies, set by the site you are on, are largely functional. Third-party cookies are different. They are placed by external services, typically advertising networks or analytics platforms, whose code is embedded on the page. When the same ad network appears on thousands of websites, its cookie follows you across all of them, recording a trail of the pages you visit.
Many browsers now block third-party cookies by default or are moving toward doing so. This has pushed the ad industry toward alternative tracking methods, which is why understanding cookies alone gives an incomplete picture.
Read cookie consent prompts carefully
Most cookie banners include an option to reject non-essential cookies, but it is often less prominent than the accept button. Taking an extra few seconds to find and select the reject or manage option on sites you visit regularly reduces third-party cookie tracking without affecting how the site works for you.
Trackers beyond cookies
A tracker is any technology that collects data about your behavior for purposes beyond the immediate page function. Some common ones include:
- Pixel trackers: Tiny, invisible images embedded in web pages or emails. When your browser loads the image, it sends your IP address and device details to the server that hosts it. Email marketers use these to know whether you opened a message.
- Local storage and session storage: Browsers allow sites to store data locally, similar to cookies but with larger capacity and different rules. Trackers can store identifiers here even if you block cookies.
- Login-based tracking: When you are signed into a Google, Facebook, or other account in your browser, those services can log your activity on any site that includes their code, such as a Like button or a Google Analytics script.
For a broader view of how one specific service builds a profile from your behavior, the article on how search engines build a profile from your queries covers the pattern in detail.
Browser fingerprinting: tracking without storage
Browser fingerprinting does not store anything on your device. Instead, a script on a webpage queries your browser for a set of technical attributes: your screen resolution, operating system, time zone, installed fonts, graphics hardware, and browser version, among others. Individually, none of these is unique. Combined, they often produce an identifier that distinguishes your device from millions of others with a high degree of accuracy.
Because nothing is written to your browser, clearing your history, deleting cookies, or using a private browsing window does not change your fingerprint. The same device, on the same network, will produce the same result.
Some browsers, such as Firefox and Tor Browser, attempt to reduce fingerprint distinctiveness by returning generic or randomized values for certain attributes. Extensions built for this purpose exist as well, though browser extensions can themselves request broad access that is worth scrutinizing before installation.
~80%
Websites using at least one third-party tracker
Web crawl studies, including research published by the Electronic Frontier Foundation, have consistently found third-party tracking code on the large majority of popular websites.
1 in 3
Top websites using browser fingerprinting scripts
Academic research into fingerprinting prevalence, including a study by researchers at Princeton University (WebTAP project), found fingerprinting scripts on a significant fraction of heavily visited sites.
Over 100
Trackers found on some major news sites
Privacy analysis tools such as Ghostery and uBlock Origin have detected over 100 separate tracking requests loading on individual pages of high-traffic media websites.
What you can realistically do
No single tool eliminates tracking entirely. A practical approach combines several modest steps that, together, reduce the amount of data collected.
At the browser level, choosing a browser that blocks trackers by default removes a significant share of third-party cookie tracking without requiring manual configuration. Enabling the browser's built-in privacy settings goes further; many of these are not turned on by default, as described in the guide to privacy settings most people never touch.
At the network level, a DNS-based blocker can stop tracker requests before they reach your browser. This addresses some fingerprinting scripts as well as cookie-based trackers.
For a structured approach to auditing your current exposure across browsers, apps, and accounts, the personal privacy audit checklist walks through each area in sequence.
Cookie consent banners, when they offer a genuine choice, are worth using deliberately. Rejecting non-essential cookies on sites that allow it reduces third-party tracking without affecting site functionality in most cases.