The NYT blows the lid on the huge amount of tracking private companies are carrying out in a mostly unregulated industry. "After spending months sifting through the data, tracking the movements of people across the country and speaking with dozens of data companies, technologists, lawyers and academics who study this field, we feel the same sense of alarm. In the cities that the data file covers, it tracks people from nearly every neighborhood and block, whether they live in mobile homes in Alexandria, Va., or luxury towers in Manhattan."