Yahoo today disclosed the contents of three National Security Letters it received in 2013 and 2015. Yahoo is the first company under reforms afforded by the USA FREEDOM Act to do so. The FBI is now required to periodically review whether non-disclosure around NSLs remains appropriate. The letters demand the target of the investigation s name, address and length of service with Yahoo for all services and accounts. Gag orders accompany the letters prohibit recipients from disclosing receipt of a NSL and from informing customers.
Source: https://threatpost.com/yahoo-discloses-contents-of-three-national-security-letters/118389/