Click through Facebook, ask Google for directions, shop on Amazon — you know you’re leaving an electronic trail. What you may not know is that hiding in the dark corners of the Internet countless data brokers and advertisers are hoovering up that data gold, watching you through a “one-way mirror.”

Third-party corporate surveillance — by companies that users don’t intend to interact with — lurks everywhere on the Internet, largely invisible to the consumer, according to a study by the Electronic Frontier Foundation, a nonprofit that advocates for digital privacy.

“Corporations have built a hall of one-way mirrors: from the inside, you can see only apps, web pages, ads and yourself reflected by social media,” the EFF report states. “But in the shadows behind the glass, trackers quietly take notes on nearly everything you do.”

The average web page shares data with dozens of third parties, according to EFF. Staying offline doesn’t protect you, either. Shopping centers now use license-plate readers and facial-recognition software to determine who goes to their brick-and-mortar stores.

The goal is to build out a full profile of a real person.

So first they have to make sure you’re you. That means looking for a piece of identifying information that’s unique, that won’t change and that can be easily obtained via cookies, IP addresses, facial recognition software, addresses, phone numbers or other methods.

“Corporations have built a hall of one-way mirrors: from the inside, you can see only apps, web pages, ads and yourself reflected by social media.”

Once they have your data, companies often pool their information because they each have only a small piece of the picture. So your details may be bought and sold. EFF warns that, “the more a user’s data is spread around, the greater the risk that they will be affected by a harmful data breach.”

Most third-party data collection in the U.S. is unregulated, but the European Union has made a legislative start with the General Data Protection Regulation. And some U.S. state and federal laws offer limited protection. But EFF advocates for more, including new laws to protect user privacy and improve transparency.

Protecting data on a consumer and corporate level is a multibillion dollar industry and growing, with Pitchbook estimating the entire market at $120.6 billion, increasing nearly 9% a year. Venture capital exits through the third quarter totaled $13.1 billion, surpassing last years’ $12.6 billion, according to Pitchbook. Blockchain is being probed as a potential tool to improve security. 

In the meantime, EFF has a few tips for users, while acknowledging that avoiding tracking is difficult and can take an enormous amount of time:

  • The choice of web browser matters. Apple’s Safari and Mozilla’s Firefox block some cookies, and extensions like EFF’s Privacy Badger and uBlock Origin add another layer of protection. Those extenders can block exposure on Google’s Chrome. And network-level filters can be installed in the home.
  •  It’s harder to block trackers on mobile phones, but the device’s settings are the first place to start, with both iOS and Android allowing users to control the permissions that each application has access to. Both have options to reset the device’s ad ID and opt out of some kinds of advertising. But if you really want to be anonymous, use a burner phone.