What purpose do National Security Letters (NSLs) serve? How do NSLs differ from subpoenas?

Question

What will be an ideal response?

Answer 1

NSLs are used in investigations of anti-international terrorism and/or clandestine intelligence purposes. They enable federal investigators to obtain information about an individual's finances, names and addresses of all financial institutions where a suspect has or has had an account, all information within a credit reporting agency's files pertaining to the target of the NSL, information from telecommunications providers as to the targeted person's wire and electronic communications – such as routing and addressing information – but not the content of the communication(s). Information can be required from banks, credit unions, pawnbrokers, travel agencies, automobile dealers, the U.S. Postal Service, casinos, consumer reporting agencies, telecommunication providers, and other financial institutions. Additionally, if the targeted person is a government employee or security clearance holder, the investigators can obtain financial records concerning travel.
Unlike subpoenas, NSL's are can only be used by federal investigative agencies specified in the statute, are limited to the securing of selected records in the custody of third parties, avoid the pre-issue control of "neutral and detached" judicial scrutiny, the record holder is required to keep the request secret, and they rely solely on the word of the requesting investigator as to the necessity for issue the NSL and the relevance of the material to an ongoing investigation.