You probably already know that you have precious little privacy, and that shadowy data brokers have built the buying and selling of people’s personal information into a multibillion-dollar industry.

But did you know this: Nobody knows how many so-called list owners and list brokers are operating nationwide. The best guess is tens of thousands.

Or this: These businesses operate largely unregulated, overseen day-to-day by no official authority.

And if they get things wrong — that is, if there’s ever need to correct files as a result of a death, divorce or similarly life-changing event — there’s pretty much nothing you can do to hold firms accountable.

Privacy was in the news recently as the Federal Communications Commission approved sweeping rules aimed at ensuring that broadband providers don’t abuse customers’ browsing history, mobile location data and other sensitive info. Service providers must get customers’ permission before using or sharing such information.

The FTC has also proposed legislation that would address some of the problems. But it has gotten nowhere.

Meanwhile, the number of data brokers continues to grow, with each firm exploiting the convergence of public records and digital technology.

“Consumers don’t realize how much information they give out,” said Suzanne Doyle-Ingram, president of the list broker Strategic List Services. “It starts with your phone service. As soon as you sign up, that information becomes available.”

After that, she said, every survey you fill out, every magazine you subscribe to, adds more pieces to the puzzle. Before long, a data broker knows your name, address, age, hobbies, interests and other details of your life that can be parsed into a variety of mailing lists, depending on a marketer’s needs.

One of the country’s largest list brokers, Nebraska’s Infogroup, told me the company is more than willing to update its records any time a consumer makes contact. All the consumer has to do is ask a business which list broker it used.

“If Infogroup is the source … they then can contact us via our website,” a representative said by e-mail.

But what if the business won’t reveal the identity of its list broker? The Infogroup representative didn’t answer.

Senny Boone, the Direct Marketing Association’s general counsel, acknowledged that “there are companies out there that may not be aware of their responsibilities.”

She said any association member is obliged to trace erroneous data to its source and make sure a correction is made. One small problem: The Direct Marketing Association has about 2,000 members. That’s only a small percentage of the tens of thousands of list owners and brokers out there.

Another thing: While Boone said the direct-marketing industry is proud of its “robust self-regulatory regime,” what we’re talking about here is the honor system. That’s not exactly the most confidence-boosting safeguard for consumer privacy.

My proposal is passage of a federal or state law that requires any business contacting consumers to disclose, upon request, the source of that contact information. People thus would have the ability to fix errors in list brokers’ databases. But I’m not holding my breath.

David Lazarus is a Los Angeles Times columnist.