a.k.a. device fingerprinting
The act of collecting personal information from computers, cell phones, and set-top boxes so as to track the users' online behavior, shopping habits, and demographics. It is the equivalent of your "digital fingerprint" and this information is sold to online advertisers who are willing to pay top dollar for granular data about people's interests and activities.
A typical computer broadcasts hundreds of details about itself when a Web browser connects to the Internet. Companies tracking people online can use those details to "fingerprint" browsers and follow their users. Computers need to broadcast certain details about their configuration in order to interact smoothly with websites and with other computers. For example, computers announce which specific Web browsers they use, along with their screen resolution, to help websites display content correctly.
Considered the next-generation of online advertising because advertisers no longer want to just buy ads but rather buy access to specific people, tracking companies are now embracing fingerprinting primarily because it is tougher to block than other common tools used to monitor people online, such as cookies (which can be deleted).
Also known as "device fingerprinting" it is legal, however there are experts who advocate that such "fingerprinting companies" who use "persistent identifiers" must let people opt-out of being tracked online. It is difficult for even sophisticated Web surfers to tell if their devices are being fingerprinted. Even if people modify their machines --adding or deleting fonts, or updating software and apps-- fingerprinters can still recognize them. There's not a method for people to delete fingerprints that have been collected which makes fingerprinting largely invisible (behind-the-screens), tough to avoid, and semi-permanent.
NetLingo Classification: Online Jargon