Data may be harvested from various sources, including census, change of address, motor vehicle-related records, user-contributed material and social networking sites, media and court reports, voter registration lists, consumer purchase histories, most-wanted lists and terrorist watch lists, bank card transaction records, health care authorities, and Web browsing histories. IBs may also purchase information from other companies (such as a credit card company). The information collected may include name, address, social security number, driver's licence number and other such identifying information, as well as occupation, property ownership, income, etc. Advertising companies are most often only interested in profiles and categories rather than personal information about an individual.
Data broker - Wikipedia