Let's be real about this -- if the N.S.A. wants data on any particular Yahoo user, or on all Yahoo users for that matter, it's not going to make one wit of difference if Yahoo encrypts its data or not. All the N.S.A. has to do is issue a national security letter, and Yahoo will cough-up whatever they got. Yahoo's encrypting the data on disk or in transit through their datacenters is little more than a pathetic attempt to lure customer's into believing that Yahoo is doing something to protect their data when, in fact, there's little Yahoo can do to prevent the N.S.A. for getting its hands on your data.