PRISM already gave the NSA access to tech giants. Here’s why it wanted more.

A new report from the Post's Barton Gellman and Ashkan Soltani reveals that the NSA has been tapping into the primary communications links that connect Yahoo and Google data centers around the world. That allowed the agency to collect metadata and content from hundreds of millions of user accounts -- including many belonging to American citizens and residents.

The NSA already had robust front door access to those companies via PRISM. So why did it need a back door?

There are some obvious reasons: The operations take place overseas, where many statutory restriction on surveillance don't apply -- and where the Foreign Surveillance Intelligence Court (FISC) has no jurisdiction. In fact, the FISC ruled a similar, smaller scale program involving cables on U.S. territory illegal in 2011. So if the NSA decides to harvest that data on foreign soil, it can skip most of the oversight mechanisms.

Data are an essentially global commodity, and the backup processes of companies often mean that data is replicated many places across the world. So just because you sent an e-mail in the U.S., doesn't mean it will always stay within the nation's borders for its entire life in the cloud...

 But the NSA may have preferred its back-door method of accessing the data because it was less visible to the technology companies holding the data. By accessing data without the knowledge of tech companies, it didn't have to worry that the volume of data iit was accessing could raise privacy alarm bells within those companies.

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