persistent identification element (PIE)

Persistent identification element (PIE) is a method of individually tagging users’ browsers for the purposes of identification and tracking.

PIE was discovered in a 2009 study,” Flash Cookies and Privacy,” which demonstrated cookies that were reappearing (respawning) after deletion. The paper revealed that 50 percent of the top 100 most popular websites used PIE to tag individual user’s browsers with a unique identifier that – unlike ordinary HTTP cookies -- cannot be easily deleted.

PIE uses a combination of JavaScript and Flash to create this tracking substitute, which is stored as a Flash cookie (also known as a locally stored object). The method makes it possible for deleted HTTP cookies to be respawned from stored data associated with the unique identifier.

 Adobe has included the option to delete and deny LSO in newer versions of Flash. However, default settings are to allow LSOs without prompting. In effect , the relative obscurity of the settings ensures that most people will not access them, leading to increased user tracking for firms and less privacy protection for users.

As with many security measures, there is a convenience versus functionality trade off:  On gaming sites, changing the default behavior of Flash for LSOs may lose game progress; on other websites, doing so may disable persistent personalization elements on Flash-based sites.

Other strong methods of avoiding browser tracking include browsing from a virtualized environment with a regularly restored snapshot or from a LiveDistro, an operating system stored on some bootable medium.

PIE was created by the online user tracking / advertising firm United Virtualities.