Yahoo is the latest technology company implicated in the US National Security Agency (NSA) Prism internet surveillance programme to call for greater transparency around its involvement.
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In June 2013, Google, Facebook, Twitter and Microsoft called on the US government to allow them to publish greater detail about requests they receive to hand over user data.
US government agencies can demand data from private companies under the Foreign Intelligence Surveillance Act (Fisa) with a national security letter (NSL).
However, NSLs prohibit the companies supplying the information from making requests public.
Now Yahoo has called on the court that approves data requests under Fisa to release documents proving the internet company “objected strenuously” to intelligence agencies accessing its data, according to the San Jose Mercury News.
The documents relate to a 2008 case in which Yahoo attempted to resist NSA demands for customer information, but its objections were overruled.
Read more about Prism and the NSA
- Security Think Tank: Prism fallout could be worse than security risks
- Security Think Tank: Prism is dangerous for everyone
- Security Think Tank: Prism – Sitting duck or elaborate honeypot?
- NSA surveillance whistleblower reveals identity
- US repeatedly hacked China, claims NSA whistleblower
- FBI spies on internet users
- UK links to US internet surveillance remain unclear
- Technology companies call for more transparency over data requests
- Compliance: The Edward Snowden, NSA program controversy continues
Yahoo argues that the release of the Fisa court's decision and the parties' briefing is necessary to inform public debate about how the court considers and examines the government's use of directives.
Under federal law the ruling and Yahoo's arguments against it have been treated as classified information.
"The directives at issue in this debate are at the centre of a robust national debate represented by countless news articles, a statement from the director of national intelligence and congressional hearings," Yahoo said.
Providing more information would "inform this debate and prevent misunderstandings", the company said.
If Yahoo succeeds in unsealing some of the court files, legal experts say, it would prove an historic development and an important step toward illuminating the arguments behind Prism.