Nonetheless, those numbers pointed to much wider use of the NSLs than the 7, 201 targets of the letters reported by the Department of Justice in 2011.

FORBES: Here's The Judge's Order Banning The FBI's Secret Requests For Companies' User Data

The letter in the case is one of the more limited types of NSLs: It asks for the name, address and length of service associated with one or more accounts.

WSJ: FBI Secretive 'National Security Letter' Demand for Phone Records Faces Rare Challenge

The decision comes on the heels of a report from Google that for the first time gave a ballpark figure of the number of its users targeted by NSLs over the last four years.

FORBES: Here's The Judge's Order Banning The FBI's Secret Requests For Companies' User Data

But Julian Sanchez, a research fellow at the Cato Institute who has tracked the NSL issue, says that NSLs sent to an Internet service like Google could still be used to de-anonymize Internet content when the FBI knows an IP address but not a name or other identifying details.

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