TechCrunch is reporting that Microsoft has successfully managed to challenge a National Security Letter (NSL) from the FBI that included a gag order. The gist is simple: according to Microsoft they received an NSL requesting "basic subscriber information" regarding an "enterprise" customer; i.e. the FBI was after the metadata of a large Microsoft client.
As is normal for NSLs, the letter banned Microsoft from disclosing to anyone that the data had been requested. Microsoft didn't think that reasonable and filed a challenge resulting in the FBI retracting its request. What's perhaps more interesting isn't that a single National Security Letter was beaten back, but how Microsoft argued its case which could, in theory, be used by others to defeat other NSLs.