The main concept is that each licensee (the user) is given a unique key which unlocks the software or allows the media to be decrypted.
The practice of traitor tracing is most often implemented with computer software, and evolved from the previous method of activation codes.
In this model, each box of software ships with a unique activation number on a sticker or label that can only be read after the package is opened, separate from the CD-ROM or a DVD-ROM.
If the user mistypes a single character in what is sometimes a very long code, the software will refuse to install and require the number to be retyped until it is correct.
Software that employs this additional security keeps a copy of the actual serial number being used in the license code.
This prevents a small business from buying one copy of expensive software and installing it on several of the computers at their location, provided they are networked.
The process of online registration is very similar to activation codes, but adds an additional step.
This allows the software manufacturers to add an additional check to their system during the installation process.
Some software that implements online registration extends this with a process commonly known as "phoning home".
In this case, the software, either each time it is used or at some preset interval such as monthly, makes another connection back to the registration server.
Serial numbers that have been identified as "pirated" (illegally distributed) are added to a blacklist on the server, a process referred to as being "burned".
This makes it very easy to "trace the traitor" and find any customers who originally gave out their activation codes.