Adnxs (AppNexus): What is it and what does it do?

Adnxs appeared as the eighth-biggest name in our Tracking the Trackers data. Here we find out as much as we can about what it does.

For an introduction to cookies and web trackers, read our guide.

What is adnxs.com?

Adnxs.com is run by AppNexus, a company that provides technology, data and analytics to help companies buy and sell online display advertising.

The technology it uses can plug into other advertising serving platforms, such as Google's Doubleclick, and "data aggregators", such as Quantcast, which provide behavioural targeting. In essence, this makes AppNexus an an "advertising exchange for advertising exchanges".

AppNexus offers a number of different services, including:

Ad exchange
An auction marketplace where advertisers can bid for ad slots on certain websites.

Data aggregator/supplier
The company collects data from a range of online and sometimes offline sources and provides data to advertisers directly or via its exchange.

Demand-side platform
Technology provider that enables advertisers to buy ad inventory from other ad exchanges.

What information is AppNexus tracking?

The company says it uses cookies and web beacons to build groups of users (segments) that are used to target advertising.

It is not entirely clear from AppNexus's website or privacy policy under what circumstances someone is likely to have an AppNexus cookie set on their browser. However, it is not too wild an assumption to make that the cookie is set when a browser visits websites that use the AppNexus service or related ad exchanges.

Web beacons may also appear on these websites and work in conjunction with the cookies to identify the types of pages a browser is visiting. It is also possible that web beacons may be included in advertising that is using the AppNexus service to provide data about the success of the adverts and whether browsers who clicked on adverts then went on to buy anything.

According to its page on cookies, information that may be tracked about about a browser include:

- a unique identifier (so a browser can be recognised when it appears on another website using AppNexus' services).
- what adverts the browser has seen.
- what page the browser was on when they saw the advert.
- when the browser saw the advert.
- whether the advert has been clicked or not.
- what type of pages the browser has visited (to build up an idea of what content might be used).
- IP Address (to infer location).

Is the data sold to third parties?

On AppNexus' website, it mentions that it allows customers to match data that has been collected through the company's services with data from other services.

This is the complicated world of cookie matching – where two services will share the same ID for a browser.

AppNexus says it only shares data when it is aggregated into a report or when required by law (this is the same for all organisations that store data).

Is the data ever matched to personally identifiable information?

No, says AppNexus.

How long is the data stored by AppNexus?

Data obtained by AppNexus are owned by their customers. Any data in the platform is retained in non-aggregated form for up to 12 months. Aggregated data, which AppNexus uses to create reports and analysis, may be stored for up to three years.

Adnxs (AppNexus): What is it and what does it do? | Cookies and web tracking

For an introduction to cookies and web trackers, read our guide. Adnxs.com is run by AppNexus, a company that provides technology, data and analytics to help companies buy and sell online display advertising.