Yahoo
said the US government threatened to fine it $250,000 a day if the search giant
failed to hand over user data.
According
to court documents, the National Security Agency (NSA) had demanded that Yahoo
comply with new surveillance rules, something the company said was
unconstitutional.
Yahoo
failed in a court challenge on the constitutionality of the order.
But
the details emerged on Thursday when a federal judge ordered the unsealing of
some material about case.
Yahoo's
general counsel Ron Bell said publication of the material was "an
important win for transparency".
Yahoo
said that