June 13, 2014: This story has been updated. It was originally published on March 7, 2013.

We've spent a lot of time this past year trying to understand how the National Security Agency gathers and stores information about ordinary people. But there's also a thriving public marketfor data on individual Americans—especially data about the things we buy and might want to buy.

Consumer data companies are scooping up huge amountsof consumer information about people around the world and selling it, providing marketers details about whether you're pregnant or divorced or trying to lose weight, about how rich you are and what kinds of cars you drive. But many people still don't know data brokers exist.

The Federal Trade Commission is pushing the companies to give consumers more information and control over what happens to their data. The White House released a report this May outlining concerns that these detailed consumer profiles might lead to race or income-based discrimination—what the White House called "digital redlining."

It's very hard to tell who is collecting or sharing your data—or what kinds of information companies are collecting. Early this year, Office Max sent a letter to a grieving father addressed to his name, followed by "daughter killed in car crash."

Here's a look at what we know—and what we don't—about the consumer data industry.

How much do these companies know about individual people?



Credit reporting giant Experianhas a separate marketing services division, which sells lists of "names of expectant parents and families with newborns" that are "updated weekly."

The companies also collect data about your hobbies and many of the purchases you make. Want to buy a list of people who read romance novels? Epsiloncan sell you that, as well as a list of people who donate to international aid charities.

A subsidiary of credit reporting company Equifax even collects detailed salary and pay stub informationfor roughly 38 percentof employed Americans, as NBC news reported. As part of handling employee verification requests, the company gets the information directly from employers.



Where are they getting all this info?

The stores where you shop sell it to them.



But thanks to California's "Shine the Light" law, researchers at U.C. Berkeley were able to get a small glimpse of how companies sell or share your data. The studyrecruited volunteers to ask more than 80 companies how the volunteers' information was being shared.




Where else do data brokers get information about me?


Public voting records, which include information about your party registration and how often you vote, can also be bought and sold for commercial purposesin some states.




Other than certain kinds of protected data—including medical records and data used for credit reports—consumers have no legal right to control or even monitor how information about them is bought and sold. As the FTC notes, "There are no current lawsrequiring data brokers to maintain the privacy of consumer data unless they use that data for credit, employment, insurance, housing, or other similar purposes."

So they don't sell information about my health?

Actually, they do.






Do companies collect information about my social media profiles and what I do online? (Updated June 12, 2014)





In fact, the effort to connect online and offline information about you is one of the hottest new trends in the data industry. Companies are increasingly trying to use information about your offline purchases to target you online.

And it's not limited to what you buy: in the 2012 elections, companies were able to match your voting record to a cookie on your computer—allowing candidates to target you with online ads based on whether you're a registered Democrat or Republican—or how much you donated to political campaigns before.

Is there a way to find out exactly what these data companies know about me? (Updated 6/12/2013)

Not really—although that's beginning to change.


Most companies offer, at best, a partial picture.

ProPublica's Julia Angwin requested information about herself from data brokers, and was "equally irked by the reports that were wrong—data brokers who thought I was a single mother with no education—as I was by the ones that were correct—is it necessary for someone to track that I recently bought underwear online?"

In September 2013, Acxiom debuted aboutthedata.com, which allows to you review and edit some of the company's marketing data on you, by entering your name, address, birth date and the last four digits of your social security number.

The Federal Trade Commission's Julie Brill tweeted that "more data brokers should follow" Acxiom's example. But the effort received mixed reviewsfrom users, privacy advocates and government regulators, the New York Times reported.

Previously, Acxiom only let customers review a smaller sliceof the information the company sells about them, including criminal history, as New York Times reporter Natasha Singer described in 2012. When Singer requested and finally received her report in 2012, all it included was a record of her residential addresses.

Other companies also offer some access. A spokeswoman for Epsilon said it allows consumers to review "high level information" about their data—like whether or not you've purchased "home furnishings" merchandise. (Requests to review this information cost $5 and can only be made by postal mail.)

RapLeaf, a company that advertises that it has "real-time data" on 80 percent of U.S. email addresses, says it gives customers "total control over the data we have on you," and allows them to review and edit the categories it associates with them (like "estimated household income" and "Likely Political Contributor to Republicans").

How do I know when someone has purchased data about me?

Most of the time, you don't.


Is there any way to stop the companies from collecting and sharing information about me? (Updated 6/12/2013)

Sometimes—but it requires a whole lot of work.

Some data brokers offer consumers the chance to "opt out" of being included in their databases, or at least from receiving advertising enabled by that company. Rapleaf, for instance, has a "Permanent opt-out" that "deletes informationassociated with your email address from the Rapleaf database."


We collected a list of data brokers that will give you copies of your data, and another list of data brokers that allow you to opt-out.

Of the 212 data brokers she identified, less than half—92—accepted opt-outs. For most of them, the op-out process was laborious. Many required her to submit some form of identification, such as a driver's license, in order to opt out. In some cases, she wrote, "I decided not to opt-out because the service seemed so sketchy that I didn't want to send in any additional information."

But she was able to clear her information from some databases: "A search for my name on some of the largest people-search websites, such as Intelius and Spokeo, yields no relevant results," she wrote.

In a 2012 privacy report, the FTC suggested that data brokers should create a centralized websitethat would make it easier for consumers to learn about the existence of these companies and their rights regarding the data they collect.

How many people do these companies have information on?



How is all of this data actually used?





In a 2012 report on privacy, the Federal Trade Commission recommended that Congress pass legislation"that would provide consumers with access to information about them held by a data broker." President Barack Obama has also proposed a Consumer Privacy Bill of Rightsthat would give consumers the right to access and correct certain information about them.






How do data brokers impact you? See the back-and-forth from 2013 Twitter chat with three privacy reporters.