The increasing awareness of, and concerns with, online tracking technologies such as cookies have led several new firms to introduce cookie alternative for tracking and identification purposes. Once such approach, know as device fingerprinting, takes advantage of all of the information a computer typically broadcasts unknowingly when going online to form a uniquely identifiable device profile.
Collecting web browser configuration information to unique identify users isn't new; it's long been used to uniquely identify users in an effort to accurately measure traffic, filter out attempts at click fraud, and customize the experience presented. Device fingerprinting startups targeting online advertising utilize a variety of techniques, including data collection scripts that execute within the browser, that help build a unique fingerprint based on a variety of factors. Because they don't rely on cookies, but rather a combination of passive (data the browser provides normally) and active (client-side code embedded in a web page that pulls additional data), they are much more difficult to bypass or defeat than cookies (see How to Fingerprint A Computer for details).
While this would seem to provide a much greater level of accuracy in tracking user activity, it's the promise of combining this fingerprinting technology with data exchanges that aggregates information about these users to further "score" these individual identities for considerations such as reputation, behavior, intention, and affinity holds great promise, as does the potential to associate these profiles with other data sources to provide more focused targeting, with greater levels of accuracy vs. cookies.
As for addressing privacy concerns, fingerprinting's increased accuracy in identifying individuals also benefits those wishing to "opt out", although the inability to effectively block fingerprinting is sure to raise concerns as its use grows. One immediately accessible technique is the "private" browsing mode already available in most browsers. As for assessing how unique your particular setup is, The Electronic Frontier Foundation has a tool, Panopticlick, that determines how unique a particular browser configurations is.
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