A device fingerprint or machine fingerprint is information collected about the software and hardware of a remote computing device for the purpose of identification. The information is usually assimilated into a brief identifier using a fingerprinting algorithm. A browser fingerprint is information collected specifically by interaction with the web browser of the device.: 878 : 1
Device fingerprints can be used to fully or partially identify individual devices even when persistent cookies (and zombie cookies) cannot be read or stored in the browser, the client IP address is hidden, or one switches to another browser on the same device. This may allow a service provider to detect and prevent identity theft and credit card fraud,: 299  but also to compile long-term records of individuals' browsing histories (and deliver targeted advertising: 821 : 9 or targeted exploits: 8 : 547 ) even when they are attempting to avoid tracking – raising a major concern for internet privacy advocates.
This section needs to be updated.(March 2020)
Basic web browser configuration information has long been collected by web analytics services in an effort to measure real human web traffic and discount various forms of click fraud. Since its introduction in the late 1990s, client-side scripting has gradually enabled the collection of an increasing amount of diverse information, with some computer security experts starting to complain about the ease of bulk parameter extraction offered by web browsers as early as 2003.
In 2005, researchers at University of California, San Diego showed how TCP timestamps could be used to estimate the clock skew of a device, and consequently to remotely obtain a hardware fingerprint of the device.
In 2010, Electronic Frontier Foundation launched a website where visitors can test their browser fingerprint. After collecting a sample of 470161 fingerprints, they measured at least 18.1 bits of entropy possible from browser fingerprinting, but that was before the advancements of canvas fingerprinting, which claims to add another 5.7 bits.
In 2014, 5.5% of Alexa top 10,000 sites were found to use canvas fingerprinting scripts served by a total of 20 domains. The overwhelming majority (95%) of the scripts were served by AddThis, which started using canvas fingerprinting in January that year, without the knowledge of some of its clients.: 678 
In 2015, a feature to protect against browser fingerprinting was introduced in Firefox version 41, but it has been since left in an experimental stage, not initiated by default.
The same year a feature named Enhanced Tracking Protection was introduced in Firefox version 42 to protect against tracking during private browsing by blocking scripts from third party domains found in the lists published by Disconnect Mobile.
At WWDC 2018 Apple announced that Safari on macOS Mojave "presents simplified system information when users browse the web, preventing them from being tracked based on their system configuration."
A 2018 study revealed that only one-third of browser fingerprints in a French database were unique, indicating that browser fingerprinting may become less effective as the number of users increases and web technologies convergently evolve to implement fewer distinguishing features.
In 2019, starting from Firefox version 69, Enhanced Tracking Protection has been turned on by default for all users also during non-private browsing. The feature was first introduced to protect private browsing in 2015 and was then extended to standard browsing as an opt-in feature in 2018.
Diversity and stability
In order to uniquely distinguish over time some devices through their fingerprints, the fingerprints must be both sufficiently diverse and sufficiently stable. In practice neither diversity nor stability is fully attainable, and improving one has a tendency to adversely impact the other. For example, the assimilation of an additional browser setting into the browser fingerprint would usually increase diversity, but it would also reduce stability, because if a user changes that setting, then the browser fingerprint would change as well.: 11
A certain degree of instability can be compensated by linking together fingerprints that, although partially different, might probably belong to the same device. This can be accomplished by a simple rule-based linking algorithm (which, for example, links together fingerprints that differ only for the browser version, if that increases with time) or machine learning algorithms.
Entropy is one of several ways to measure diversity.
Sources of identifying information
Applications that are locally installed on a device are allowed to gather a great amount of information about the software and the hardware of the device, often including unique identifiers such as the MAC address and serial numbers assigned to the machine hardware. Indeed, programs that employ digital rights management use this information for the very purpose of uniquely identifying the device.
Even if they aren't designed to gather and share identifying information, local applications might unwillingly expose identifying information to the remote parties with which they interact. The most prominent example is that of web browsers, which have been proved to expose diverse and stable information in such an amount to allow remote identification, see § Browser fingerprint.
Diverse and stable information can also be gathered below the application layer, by leveraging the protocols that are used to transmit data. Sorted by OSI model layer, some examples of such protocols are:
- OSI Layer 7: SMB, FTP, HTTP, Telnet, TLS/SSL, DHCP
- OSI Layer 5: SNMP, NetBIOS
- OSI Layer 4: TCP (see TCP/IP stack fingerprinting)
- OSI Layer 3: IPv4, IPv6, ICMP, IEEE 802.11
- OSI Layer 2: CDP
Passive fingerprinting techniques merely require the fingerprinter to observe traffic originated from the target device, while active fingerprinting techniques require the fingerprinter to initiate connections to the target device. Techniques that require to interact with the target device over a connection initiated by the latter are sometimes addressed as semi-passive.
The collection of large amount of diverse and stable information from web browsers is possible thanks for most part to client-side scripting languages, which have been introduced in the late '90s. Today there are several open-source browser fingerprinting libraries, such as FingerprintJS, ImprintJS, and ClientJS, where FingerprintJS is the most updated and supersedes ImprintJS and ClientJS to a large extent.
|Browser family||Property deletion (of navigator object)||Reassignment (of navigator/screen object)|
A browser unique combination of extensions or plugins can be added to a fingerprint directly.: 545 Extensions may also modify how any other browser attributes behave, adding additional complexity to the user's fingerprint.: 954 : 688 : 1131 : 108 Adobe Flash and Java plugins were widely used to access user information before their deprecation.: 3 : 553 
:visited.: 5 Typically, a list of 50 popular websites is sufficient to generate a unique user history profile, as well as provide information about the user's interests.: 7,14 However, browsers have since then mitigated this risk.
Canvas and WebGL
Canvas fingerprinting uses the HTML5 canvas element, which is used by WebGL to render 2D and 3D graphics in a browser, to gain identifying information about the installed graphics driver, graphics card, or graphics processing unit (GPU). Canvas-based techniques may also be used to identify installed fonts.: 110 Furthermore, if the user does not have a GPU, CPU information can be provided to the fingerprinter instead.
Specialized APIs can also be used, such as the Battery API, which constructs a short-term fingerprint based on the actual battery state of the device,: 256 or OscillatorNode, which can be invoked to produce a waveform based on user entropy.: 1399
Mitigation methods for browser fingerprinting
Different approaches exist to mitigate the effects of browser fingerprinting and improve users' privacy by preventing unwanted tracking, but there is no ultimate approach that can prevent fingerprinting while keeping the richness of a modern web browser.
Offering a simplified fingerprint
This section needs to be updated.(March 2020)
Users may attempt to reduce their fingerprintability by selecting a web browser which minimizes availability of identifying information such as browser fonts, device ID, canvas element rendering, WebGL information, and local IP address.: 117
As of 2017 Microsoft Edge is considered to be the most fingerprintable browser, followed by Firefox and Google Chrome, Internet Explorer, and Safari.: 114 Among mobile browsers, Google Chrome and Opera Mini are most fingerprintable, followed by mobile Firefox, mobile Edge, and mobile Safari.: 115
Offering a spoofed fingerprint
Spoofing some of the information exposed to the fingerprinter (e.g. the user agent) may allow to reduce diversity,: 13 but the contrary could be also achieved if the mismatch between the spoofed information and the real browser information differentiates the user from all the others who do not use such strategy.: 552
Spoofing the information differently at each site visit, for example by perturbating the sound and canvas rendering with a small amount of random noise, allows to reduce stability.: 820,823  This technique has been adopted by the Brave browser in 2020.
Using multiple browsers
Different browsers on the same machine would usually have different fingerprints, but if both browsers aren't protected against fingerprinting, then the two fingerprints could be identified as originating from the same machine.
- Anonymous web browsing
- Web tracking
- Internet privacy
- Fingerprint (computing)
- Browser security
- Browser sniffing
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- Panopticlick, by the Electronic Frontier Foundation, gathers some elements of a browser's device fingerprint and estimates how identifiable it makes the user
- Am I Unique, by INRIA and INSA Rennes, implements fingerprinting techniques including collecting information through WebGL.
- Partial database of websites that have used canvas fingerprinting