There are two approaches. First is technical. Encrypt everything on originating devices and store the encrypted copy to which Microsoft would have no key (not

There are two approaches. First is technical. Encrypt everything on originating devices and store the encrypted copy to which Microsoft would have no key (not even escrowed one). Not like this works for all cases, but a lot of data - like browsing history or WiFi AP passwords - does not require server-side processing. Another is legal approach. Have sane privacy policies - not "we'll use your data as necessary" - and make sure users opt-in. Not like this also works - certainly not against all adversaries, but at least you can sue.