but across the ocean in london, private activist smari mccarthy says, hold on, some of these free services may be costing us dearly. >> if you're not paying for the product, you're not the customer, you're the product itself. >> reporter: what he means is this. for generations, americans thought of letters as private and many of us still see e-mails as kind of like that. but they're actually much more like postcards, easily read by anyone or any company between you and the person that you're sending this message to. and huge e-mail companies with millions of users do just that. with powerful computers, they scan every word for clues to help them sell precisely targeted ads, so if, for example, you write kayak in several messages, soon you may seen ads for river trips. mention "cars," and you'll get the latest models burning across your desktops. if any doubts, in a recent court