You’ve probably never heard of many of the data firms registered under a new law, but they’ve heard a lot about you. A list, and tips for opting out.

It’s no secret that your personal data is routinely bought and sold by dozens, possibly hundreds, of companies. What’s less known is who those companies are, and what exactly they do.

Thanks to a new Vermont law requiring companies that buy and sell third-party personal data to register with the Secretary of State, we’ve been able to assemble a list of 121 data brokers operating in the U.S. It’s a rare, rough glimpse into a bustling economy that operates largely in the shadows, and often with few rules.

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