Cool system.

1. The moment you visit a website or app with ad space, it asks an ad tech company to determine which ads to display for you.
2. This ad tech 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 information like your unique advertising ID, your GPS coordinates, IP address, device details, inferred interests, demographic information, and the app or website you’re visiting. The information in bid requests is called “bidstream data” and typically includes identifiers that can 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 the ad space.
5. The highest bidder gets to display an ad for you, but advertisers (or the adtech companies that represent them) can collect your bidstream data regardless of whether or not they bid on the ad space.

You'll never guess what it's being used for.