The 100 ms story, then a quiz
Why it matters Every time an advert loads on a page, a fast auction may share details about you with many companies, including ones that do not win. This story ties together everything in this module: IDs, pixels, scripts and data brokers.
The 100 ms story
Imagine an auction house where your visit is the item for sale, and the bidding is over in the blink of an eye, about a tenth of a second (100 milliseconds). Here is what happens when you open an article on news.example that has an ad slot. The timings are rough and only illustrate the order; real auctions vary:
Real-time bidding (RTB): a way of selling ad space one visit at a time, by holding an automatic auction while the page loads.
- 0 ms: the page asks for an ad. An ad script on news.example contacts an auctioneer working for the site, often called a supply-side platform (SSP).
- About 10 ms: the bid request. The auctioneer writes a description of the visit: the page address, the ad size, your device and browser, a rough location from your IP address, and any IDs it has for you, such as a cookie ID, a mobile advertising ID or a hashed-email ID.
- About 20 ms: sent to many bidders. That bid request goes out to many buyers at once, often through demand-side platforms (DSPs), which bid for advertisers.
- 20 to 80 ms: the bidders decide. Each bidder looks up what it knows about those IDs. It may add details bought from data brokers, such as "likely new parent" or "interested in cars", and chooses a price.
- About 90 ms: the winner. The highest bid wins, and the winner's advert is sent to your browser.
- Afterwards: pixels fire. The advert and the page load tracking pixels to confirm it was shown, and later whether you clicked or bought.
Data broker: a company that collects information about people from many sources, such as apps, shops, public records and other brokers, and sells profiles or audience labels.
The part that matters most
Only one bidder wins, but every bidder received the bid request. Losing bidders still learned that this ID read this article at this time from roughly this place. Repeated across a day of browsing, those snippets build up a profile.
To make IDs line up between companies, ad firms also run cookie syncing: quietly exchanging their own IDs for you, often through more pixels, so that "user 8f31c2" at one company is known to be "user b77e05" at another.
What cuts the story short
- Blocking third-party cookies and trackers removes many of the IDs in step 2.
- Fingerprinting defences stop new IDs being made up from your device.
- Declining app tracking zeroes the mobile ID; email aliases break hashed-email matching.
- GPC and honest consent choices ask the site not to share at all.
Recap
- An ad slot can trigger an auction that finishes in about 100 ms.
- The bid request carries the page, device, rough location and your IDs.
- Every bidder receives it, winner or not, and brokers enrich it.
- Each defence in this leg removes one ingredient from the bid request.
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