A request by major technology firms to disclose more about US intelligence services' data requests would "cause serious harm to national security," the government said in a court filing Wednesday.
The Justice Department, responding to petitions from major US Internet firms, said it opposes the move for more transparency in the role of the companies in vast data collection programs.
The requests "would permit damaging disclosures that would reveal sources and methods of surveillance potentially nationwide," said the filing to the US Foreign Intelligence Surveillance Court, a special body which handles secret government requests.
Yahoo, Google, Facebook and Microsoft are among the firms which have asked for permission to publish the numbers of national security data requests they receive, hoping this would reassure customers that the role of the firms is limited.
But the Justice Department's 33-page brief, which included heavy redactions in the public version to delete specific names, said the government has taken steps to be more transparent but that some information must remain classified and secret.
It said the government agreed to publish an annual report which includes an aggregate number of requests under the Foreign Intelligence Surveillance Act (FISA).
But this will not be broken down on a company basis, and accordingly "will not provide our adversaries with a roadmap to the existence or extent of government surveillance of any particular provide or communications platform."
It added that "revealing FISA data on a company by company basis would cause serious harm to national security," and that this is the reason it is classified.
The brief also disputed claims that the companies have a constitutional right to publish the information, saying such restrictions on classified information are "well-settled."
At a Senate hearing on Wednesday, the top US intelligence official reiterated these concerns.
James Clapper, director of national intelligence, said the government has no objection to the release of the total number of government requests but that a company-by-company breakdown "gives the adversaries, the terrorists, the prerogative of shopping around for providers that aren't covered."
Google, Facebook and Yahoo are among major Internet companies identified as participants in the PRISM program, described as a vast surveillance operation aimed at finding foreigners who are threats to the government. Other firms in the program included Microsoft, Apple and AOL.
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