Online Behavioral Ads Fuel the Surveillance Industry—Here’s How

A global spy tool exposed the locations of billions of people to anyone willing to pay. A Catholic group bought location data about gay dating app users in an effort to out gay priests. A location data broker sold lists of people who attended political protests. 

What do these privacy violations have in common? They share a source of data that’s shockingly pervasive and unregulated: the technology powering nearly every ad you see online. 

Each time you see a targeted ad, your personal information is exposed to thousands of advertisers and data brokers through a process called “real-time bidding” (RTB). This process does more than deliver ads—it fuels government surveillance, poses national security risks, and gives data brokers easy access to your online activity. RTB might be the most privacy-invasive surveillance system that you’ve never heard of.

What is Real-Time Bidding?

RTB is the process used to select the targeted ads shown to you on nearly every website and app you visit. The ads you see are the winners of milliseconds-long auctions that expose your personal information to thousands of companies a day. Here’s how it works:

1. The moment you visit a website or app with ad space, it asks a company that runs ad auctions to determine which ads it will display for you. This involves sending information about you and the content you’re viewing to the ad auction company.
2. The ad auction company packages all the information they can gather about you into a “bid request” and broadcasts it to thousands of potential advertisers. 
3. The bid request may contain personal information like your unique advertising ID, location, IP address, device details, interests, and demographic information. The information in bid requests is called “bidstream data” and can easily be linked to real people. 
4. Advertisers use the personal information in each bid request, along with data profiles they’ve built about you over time, to decide whether to bid on ad space. 
5. Advertisers, and their ad buying platforms, can store the personal data in the bid request regardless of whether or not they bid on ad space. 

A key vulnerability of real-time bidding is that while only one advertiser wins the auction, all participants receive the data. Indeed, anyone posing as an ad buyer can access a stream of sensitive data about the billions of individuals using websites or apps with targeted ads. That’s a big way that RTB puts personal data into the hands of data brokers, who sell it to basically anyone willing to pay. Although some ad auction companies have policies against selling bidstream data, the practice remains widespread. 

RTB doesn’t just allow companies to harvest your data—it also incentivizes it. Bid requests containing more personal data attract higher bids, so websites and apps are financially motivated to harvest as much of your data as possible. RTB further incentivizes data brokers to track your online activity because advertisers purchase data from data brokers to inform their bidding decisions.

Data brokers don’t need any direct relationship with the apps and websites they’re collecting bidstream data from. While some data collection methods require web or app developers to install code from a data broker, RTB is facilitated by ad companies that are already plugged into most websites and apps. This allows data brokers to collect data