What is a data broker, and why have you never heard of them?

A data broker collects, packages and sells personal information about people who are not its direct customers. You never signed up — yet your address, household, interests and habits may be on file.

The data comes from public records, loyalty programmes, app SDKs, ad-tech real-time bidding and other brokers. It is then resold for marketing, scoring and identity verification.

Because you were never the customer, the only leverage you have is the law: erasure and opt-out rights. Used broker-by-broker, that is the service Withheld provides.