Reporting by the Wall Street Journal last summer narrowed the possible recipients of the NSL in question to a small cell phone firm called Credo Mobile.
The USA PATRIOT Act expanded the purpose of National Security Letters (NSL) to allow government agencies to use them to request any data relevant to an investigation of terrorism or an intelligence activity without court oversight.
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.