Fingerprinting is a practice in which websites identify a particular browser (and by extension, a particular user) by collecting and combining distinguishing features of the browser and underlying operating system. Elements of a fingerprint might include, for example:

• the browser version

• the timezone and preferred language

• the set of video or audio codecs that are available on the system

• the fonts installed on the system

• the state of the browser’s settings

• the computer’s display size and resolution

A website can retrieve information like this by executing JavaScript and CSS on the device, and by combining this data can often create a unique fingerprint for a browser, which can then be used to track users across the web.

Web standards are designed in such a way as to minimize the ability of a website to collect identifying information, and browsers typically add their own protections as well.

See also

• Cover Your Tracks: a tool to show the data a website can use to fingerprint your browser.

• Mitigating Browser Fingerprinting in Web Specifications: best practices for specification authors to prevent fingerprinting.