Yahoo is the latest technology firm to reveal statistics on US government surveillance requests.
The disclosures follow revelations that the US National Security Agency (NSA) obtained access to the systems of top internet firms as part of a previously undisclosed surveillance programme called Prism.
Earlier this week, the major technology firms at the centre of the revelations by whistleblower Edward Snowden – Facebook, Microsoft and Apple – opted to reveal the number of requests they had received.
The companies had all urged the US government to allow them to reveal these data requests to counter the allegations that they had provided direct access to their systems as part of the Prism programme.
Yahoo said it had received up to 13,000 data access requests in the past six months, but like the other firms is not allowed to say how many of those were made through secret national security letters.
The firm’s chief executive, Marissa Mayer, called on the US government to reconsider its stance on this issue in a blog post.
“Like all companies, Yahoo cannot lawfully break out FISA [Foreign Intelligence Surveillance Act] request numbers at this time because those numbers are classified,” she wrote.
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Facebook said it had received up to 10,000 requests in the second half of 2012, while Microsoft said it had received up to 7,000 criminal and national security warrants, subpoenas and orders affecting between 31,000 and 32,000 consumer accounts in the same period.
Apple stated that it had received 4,000-5,000 data requests since December 2012.
In contrast, both Twitter and Google have elected not to publish their own totals, arguing that lumping all types of data requests together would be "a step backward”, according to The Verge.
Yahoo said it planned to issue later this summer its first global law enforcement transparency report, which will cover the first half of the year.
“As always, we will continually evaluate whether further actions can be taken to protect the privacy of our users and our ability to defend it,” Mayer wrote in her blog post.