For the six months ending December 31, 2012, the total number of user-data requests Facebook received from any and all government entities in the U.S. (including local, state, and federal, and including criminal and national security-related requests) - was between 9,000 and 10,000. These requests run the gamut - from things like a local sheriff trying to find a missing child, to a federal marshal tracking a fugitive, to a police department investigating an assault, to a national security official investigating a terrorist threat. The total number of Facebook user accounts for which data was requested pursuant to the entirety of those 9-10 thousand requests was between 18,000 and 19,000 accounts.
With more than 1.1 billion monthly active users worldwide, this means that a fraction of one percent of Facebook user accounts were the subject of any kind of U.S. state, local, or federal U.S. government request (including criminal and national security-related requests) in the past six months.
Microsoft said that for the last six months of 2012 it received between 6,000 and 7,000 criminal and national security warrants, subpoenas and orders affecting between 31,000 and 32,000 consumer accounts from local, state and federal U.S. governmental entities.
Both Facebook and Microsoft are fighting an expanding public backlash after a U.S. government contractor revealed it was among nine Internet giants that turned over user data to the secret National Security Agency surveillance program PRISM.
Apple, Google, Twitter and Yahoo, have also denied claims the NSA could directly access their servers. US authorities have said the program helped prevent terror attacks.
Google's "transparency report" on government requests does not include national security requests under the Foreign Intelligence Surveillance Act (FISA) that authorized PRISM. But the company said that it wants to publish aggregate numbers of national security requests, including FISA disclosures, separately.
Twitter is still not participating in Prism, although the U.S. government said it will likely be forced to comply.