It is the same with smart phones. Even if you don't install any apps or link any of your profiles (fb, g+, etc) all it takes is for one person you know to upload their address book to "find their friends" and suddenly there is linked: your phone #, email, fb (your picture included), g+, all in one spot, all without your permission or knowledge.

Even if you try and secure your data and privacy, unless everyone you know does the same thing it is pointless.