Strangers put a price on your life and labelled you easy moneyData brokers have detailed files on you. Here’s what’s in them — and how it impacts you

In the United States there are companies that make a living out of knowing you. They never ask you a question, yet they know when you last logged into your computer and how much you have spent on clothes over the past few years.

Half the file is guesswork

These companies are called data brokers, and the best known are Acxiom and Epsilon. Acxiom says it holds profiles of roughly 95% of American adults; Epsilon claims data on virtually every marketable US household.

They gather records from public documents, commercial databases and other brokers, and compile them into a file that follows you for life — and keeps going after you die.

Much of it, though, is inferred. One person's report contained six different, contradictory guesses at their age.

Your phone, TV and car all snitch

Your phone's advertising ID, your smart TV's tracking identifier, your home's IP address, your car's vehicle identification number — the brokers can hold them all. With those numbers, clients can match your behaviour across every device you own.

Your money gets estimated too. Brokers cannot see your bank account, but from where you live and what you have bought they model what you earn, what you have saved and what you are worth.

Even health gets inferred. With no access to your medical records they still guess how well you sleep, whether you smoke, your body mass index — and your religion, ethnicity and politics while they are at it.

What you are worth is what you will do next

Epsilon sorts people into one of 26 'NICHES' codes with names like 'Easy Street', 'Mid Life Munchkins' and 'Big Spender Parents'. It also tags people by how profitable they are, with labels such as 'Best Profit Margin'.

Acxiom calculates a 'lifetime value score'. For auto, home and health insurers it runs from 0 to 200,000, and the higher the number, the more profit you are expected to bring.

In a buyer's hands those labels become real: insurers use them to price a company's employees, lenders use them to spot someone who may need a financial lifeline and then offer a loan at punishing interest, banks use them to push credit monitoring you never needed.

Opting out is hard. Brokers get most of their data from other companies, not from you — you never signed up. And opting out clears your file with one broker only. The copies already sold to dozens of others are not coming back.