If you’re a registered voter and surf the web, one of sites you visit has almost certainly placed a tiny piece of data on your computer flagging your political preferences.
That piece of data, called a cookie, marks you as a Democrat or Republican, when you last voted, and what contributions you’ve made. It also can include factors like your estimated income, what you do for a living, and what you’ve bought at the local mall. [cont.]
Lois Beckett, Pro Publica