Microsoft successfully fought a national security letter from the FBI that requested a customer's data and barred the company from telling the customer about it, according to court documents that were unsealed on Thursday.
The FBI sent the letter late last year, seeking "basic subscriber information" about an account linked to one of Microsoft's enterprise (corporate or government) customers, Microsoft general counsel Brad Smith wrote in a company blog post Thursday.
The national security letter came with a gag order that barred Microsoft from disclosing the FBI's request to the customer -- or to anyone else, for that matter.
Microsoft filed a challenge to the gag order in federal court in Seattle. As Smith put it, the company argued the nondisclosure order "was unlawful and violated our Constitutional right to free expression."
After that, the FBI withdrew its letter.
A U.S. district court in Seattle unsealed the documents related to the challenge on Thursday, though the name of the enterprise customer was redacted.
As Smith noted in his post, Microsoft announced in December that it would challenge gag orders on such requests from authorities going forward. He called the FBI case "an important and successful step to protect Microsoft's enterprise customers regarding government surveillance."
However, losing the battle with Microsoft didn't stop the FBI from getting the information it wanted.
The documents published on Thursday state the FBI received the information directly from the Microsoft customer "in a way that maintains the confidentiality of the underlying investigation."