For those who are unfamiliar with NSLs, a brief overview. National Security Letters are instruments used by law federal law enforcement agencies to obtain data about users without a warrant. NSLs are usually accompanied with a gag order that prevents the entity being requested to release information from speaking publicly about the request.
The use of the letters has been in controversy since its inception but received a major overhaul that saw great expansion with implementation of the Patriot Act.
This is the first transparency report Microsoft has issued to date and many advocates have expressed concerns about the amount and type of information Microsoft can collect on Skype users. This report, while not addressing many of their concerns, does indicate that the old-dog is trying to learn a new trick from the likes of Google and Twitter.