In its latest transparency report, Google revealed that the FBI used National Security Letters (NSLs) to obtain information about thousands of its users between 2009-2012. The Justice Department did not allow Google to publish exact numbers, but only a broad range. Still, this data is helpful because the FBI’s use of NSLs is shrouded in secrecy, which the FBI enforces through gag orders on NSL recipients. Inspector General reports from 2007 and 2008 revealed widespread abuse and mismanagement of NSLs by the FBI from 2003 through 2006.
See Google’s latest transparency report here: http://googlepublicpolicy.blogspot.com/2013/03/transparency-report-shedding-more-light.html
Learn more about NSLs here: https://www.aclu.org/national-security-technology-and-liberty/national-security-letters
Read the Inspector General's report on NSL usage from 2003-2006 here: http://www.justice.gov/oig/special/s0703b/final.pdf
Read the Inspector General's report on NSL usage in 2006 here: http://www.justice.gov/oig/special/s0803b/final.pdf