Device fingerprinting is a technique where various small bits of information is collected from a computer and combined into a uniquely identifying set of information. With enough information, this fingerprint can be considered globally unique. A study by the Electronic Frontier Foundation (EFF) concludes that it should be possible to create a globally unique fingerprint from the information exposed by a web browser.
With a globally unique fingerprint, the same computer—and thus it’s user—can be reidentified across different contexts that would otherwise not be able to share information between them. Contexts such as different web advertisement networks, social networking sites, and a locally running program’s online systems. Being able to globally identify—and even reidentify at a later time—a user raises serious privacy concerns.
Computers especially are with time configured with subtle differences that make them unique. In the context of web browsers, this information can include: User‐Agent string (the browser make and version), the plug‐ins and fonts installed on the system, browser settings such as privacy and language options (as exposed in requests), IP address, and more.
The EFF has a online tool that exposes some of the information that can be collected by a web site through the standard features of a web browser. Another alternative is BrowserLeaks’ fonts tester. These tools can be used to observe the effect of the Fluxfonts program.