The existence of the legal dispute between Microsoft and the FBI became public when court documents related to the case was unsealed on Thursday.
The documents reveal that FBI agents served Microsoft with a NSL agent at some point in 2013 for information on one of Microsoft’s enterprise customers. That customer, whose name is not revealed, is said to have used a business version of Microsoft’s Office 365, a cloud-based version of the company’s word processing, spreadsheet and slideshow programs as well as e-mail and calendar services.
As is customary in NSLs, the FBI ordered Microsoft not to disclose it had been served with the letter.
Shortly after being served with the letter, Microsoft filed a challenge in court claiming the letter violated the First Amendment. Both Microsoft and the FBI entered into an agreement last October to drop the challenge after the agency received the information it sought directly from the customer, according to court documents.
The agreement reached between Microsoft and the government stated that neither party would “oppose a motion to unseal redacted versions of this Stipulation and the Petition” within six weeks. The documents released on Thursday came seven months after said agreement, and the remainder of the court docket continues to be sealed.
The case demonstrates a rare public acknowledgement of an American tech company challenging the government on the legitimacy of a NSL. With the exception of a small webhost, virtually no company challenged a NSL on the record until last year.
Last year, a federal judge found that the FBI’s use of NSLs violated the Constitution. U.S. District Judge Susan Illston ordered the government to stop issuing NSLs across the board, and further ordered federal agencies to stop enforcing a gag order on letters that had already been issued.
The date of the NSL that the FBI served on Microsoft was redacted in court documents released on Thursday; however, the FBI did not enforce a gag order on the company that would have prevented Microsoft from disclosing the letter to its attorneys.
Document: Microsoft challenges FBI national security letter (October 2013)
Ars Technica: FBI withdraws national security letter against Microsoft