The FBI has been ordered to hand over further information on its Carnivore email surveillance system.
US District Judge James Robertson told the agency that it would have to hand over more records about the system, which is installed at internet service providers to monitor emails.
The FBI claims that it only captures emails and other online information after obtaining a court order, but the Electronic Privacy Information Centre (Epic) is worried about potential abuse.
The documents wanted by the court are the result of an action in July 2000 under the Freedom of Information Act to examine Carnivore-related material.
The FBI also has to come up with more information about a network traffic management device called EtherPeek, which privacy advocates are also worried about.
The Bureau had withheld some documents from Epic producing a search of 1,957 pages of material but releasing only 1,665 pages which covered the legal and policy implications of the technology.
Epic general counsel David Sobel said that the FBI was "very grudging" about releasing any Carnivore information.
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