Companies that sell personal information are known as data brokers. They collect data from various sources to create a detailed image of the user, which they then sell. Selling this type of information is big business: the industry is worth $200 billion per year, and there are up to 4,000 brokerage firms worldwide. Experian, Equifax, Acxiom, and Epsilon are the most well-known data brokers.

Data brokers have been chastised for their lack of transparency: they are uninterested in communicating with the people whose data they collect, analyse, and sell for profit.