Explainer
Post date
16th April 2026
When it comes to the conversation of advertising technologies (AdTech), you probably typically think about tracker pixels and cookies. However, there is another pernicious tracking technique lurking in how your browser and devices communicate on the internet.
That technique is called digital fingerprinting. This explainer will cover what fingerprinting is, how it works, and why it matters.
Fingerprinting is the automatic collection of individual users’ browser and/or device data (e.g., IP address, browser version, Operating System) to create a unique ‘fingerprint’ for that user. This automatic data collection happens at the moment a user accesses a website or app. Typically, it’s not possible for a user to block this information being shared and devices connected to the internet will provide this information when it is requested.
Examples of data that may be automatically collected includes:
On the surface, data like screen size (or more accurately canvas size, as in the size of browser window) and browser data may appear generic and non-identifiable; however, the likelihood of two individuals having the exact same combination of browser and device fingerprint data is so statistically low that individual users are often unique, and consequently identifiable.
You can find out just how unique your device fingerprint using an online tool like one of these:
Photo by Marten Newhall on Unsplash
There can be practical and justified uses for fingerprinting. Websites and services may need to know certain information about a user’s device in order to appropriately display the content and its layout (e.g. responsive design which allows a website to adapt to whether a phone, tablet or PC is being used)
Or, an online banking website might need to uniquely identify a user to protect against fraud. Unique device identifier data may be needed to distinguish between a trusted user/device versus a potential bot or hacker accessing the site from an entirely different region.
Crash reporting services may also use this type of data, as an app may seek to identify which devices or browsers lead to a higher rate of issues, or seek to understand the geographic breakdown of app crash reports to ‘improve’ services and develop aggregated analytics for prioritising improvements.
While it may not be a problem for an individual website to know that a user is using the mobile version of the site in the GB region, functional reasons for data collection leave the door open to potentially pernicious uses of the same data.
Photo by William Warby on Unsplash
A user may accept the collection of their fingerprint data for functional reasons (like crash reporting), but they might not have understood the risk that this data could be used for advertising purposes. Just like cookies, collecting user data through fingerprinting techniques requires the user’s consent. But, because fingerprinting can occur invisibly in the background the moment a user navigates to a website or opens an app, data can be automatically collected before user consent is obtained.
This issue of consent raises wider concerns around the lack of user control. Fingerprinting techniques make it harder for users to both detect what data is being collected about their online activity, and to prevent it happening. Some data that can be used for fingerprinting is sent out without even being requested, meaning that its collection is hard to detect. Even when information must be requested, it may be hard to know when requests are legitimate or not.
While it’s possible to delete cookies from your device, fingerprinting tracks more permanent digital identifiers that a user cannot so easily wipe, such as hardware specifications and browser settings. This type of hardware data can be harder to modify and effectively impossible to delete. Additionally, fingerprinting is harder for browsers and extensions to block, so ‘even privacy-conscious users will find this difficult to stop’.
In the end, fingerprinting is an unfair means of tracking users online that is intrusive, invasive, and prevents control over how information is collected.
Options for how to protect against fingerprint tracking largely involve having to make potentially difficult trade offs - ad blockers may sufficiently block some tracking scripts, but they can’t easily block fingerprinting tracking due to fingerprinting being so embedded in the service of browsers and devices. Options include:
The limited control you, the user, have ultimately demonstrates how we’re in the hands of others who get to decide how websites and apps work, such as the amount and type of fingerprint data they collect. The invisible and embedded nature of fingerprinting risks deep tracking and surveillance of users’ online activity and behaviour. With companies like Google able to change their fingerprinting policies at will, and users having to potentially accept a distinct loss in functionality in order to have a tracker-free experience, we are reminded of the need to always be aware of the power imbalances at play in how the internet (and its reliance on advertising) is designed.
Glossary
Ads are "targeted" when they are aimed at an audience with specific traits based on the product or service that is being advertised.
Ads are "personalised" when they are targeted to a specific person based on their perceived or inferred interests or characteristics. These interests and characteristics are themselves derived from previous online activity, such as visited websites or apps used.
A plugin that extend the functionnalities of your browser. Addons are browser specific, an addon for Firefox might not be available for Chrome. Addons can be nefarious, don't install anything without prior research.
Used to identify your online activities. A website or tracking firm gets your browser or mail app to download an invisible image, that is linked to a unique tracking object stored on the server, thereby disclosing to the server that you have undertaken an activity. When in an email, it indicates to the server that you have opened the email.
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