The FBI has provided details about a controversial technology that law enforcement officials began using recently to uncover evidence in e-mail.

Nicknamed Carnivore the FBI has used the technology in about 25 cases over the past year to assist them in criminal and national security investigations.

The FBI started developing Carnivore about three years ago, when law enforcement officers began seeking and obtaining court orders to intercept e-mail as part of their investigations.

Some were requests to track only the identity of a person with whom a suspect was communicating, while other requests were to uncover the full content of

The system works by intercepting part of the stream of packets that moves across the network. The data goes to an interface, and from there the FBI gets a copy of the data in question.

The system then puts the data through a filter that is configured to comply with the court order.