What Is Third-Party Data?
Third-party data is collected by organisations that have no direct relationship with the individuals represented in the dataset.
Data brokers, analytics aggregators and ad networks compile behavioural signals, demographic inferences and interest categories from thousands of websites and apps, package them into audience segments, and sell access to any advertiser willing to pay.
Unlike first-party data, which you gather yourself from your own customers, third-party data involves an unknown chain of collection that the end consumer is rarely aware of.
Historically, third-party data powered the programmatic advertising ecosystem. Advertisers could buy a segment labelled "in-market for a vehicle" or "frequent traveller" and use it to target display ads across the internet.
The appeal was scale: access to millions of profiles without needing to build your own audience. The trade-off was always accuracy and recency.
Third-party data is often months old by the time it reaches an advertiser, and because the same segments are available to every competitor in your category, there is no unique advantage to buying them.
The decline of third-party data has been accelerating sharply. Safari and Firefox have blocked third-party cookies for years. Google has been phasing out third-party cookie support in Chrome progressively.
Privacy regulations such as GDPR in Europe and POPIA in South Africa impose strict requirements on how personal data is collected and shared.
Many third-party datasets were assembled under consent conditions that would not satisfy modern regulatory standards, creating legal exposure for the advertisers who use them.
For South African businesses, the practical impact is clear. Programmatic campaigns that relied on third-party audience segments are seeing declining match rates, higher frequencies to fewer unique users, and weaker attribution.
The response from forward-thinking marketers is to invest in owned data assets: CRM programmes, email lists, loyalty schemes and on-site behavioural data that produce a proprietary view of the audience.
Third-Party Data In Practice
A Durban-based financial services company running a display campaign targeting "homeowners considering a second bond" would previously have purchased this segment from a data broker and activated it across the Google Display Network.
Today, that same segment is less reliable because many of the tracking signals that built it no longer fire consistently as browsers block cookies. The advertiser sees the same spend but a smaller, less representative audience and weaker conversion rates.
The smarter approach is to replace that third-party segment with a combination of contextual targeting on property and finance content websites, a first-party CRM audience of existing customers who match the profile, and zero-party data collected through a mortgage calculator tool on the company's own website.
Each of these alternatives is more accurate, more durable and fully compliant with POPIA. Third-party data is not gone entirely, but its strategic importance is diminishing rapidly in the South African market.
How third-party data works
Third-party data is information about people collected by an organisation that has no direct relationship with them, aggregated from many sources and sold or licensed for targeting. Unlike first-party data, which you gather from your own customers, third-party data is bought in to reach audiences you do not already have relationships with, and it powered much of the cross-site behavioural targeting in digital advertising. Its appeal was scale and reach; its weaknesses were accuracy, since inferred data is often wrong, and provenance, since consent for its collection was frequently unclear. It is exactly this category that privacy regulation and the decline of third-party cookies are eroding, which is reshaping how advertising targets and measures audiences.
The decline of third-party data
Third-party data is fading for two connected reasons: privacy law increasingly requires clear consent that aggregated third-party collection often lacked, and browsers are removing the third-party cookies that made cross-site tracking work. The result is that advertisers can no longer rely on bought audience data the way they once did. The response is a shift towards first-party data collected directly with consent, which is more accurate and durable; contextual targeting based on page content rather than personal history; and privacy-preserving, modelled measurement. For businesses the practical move is to invest in owned data and direct customer relationships, since these do not depend on a third-party ecosystem that is being dismantled regardless of any single timeline.
FAQ
Is third-party data still useful for South African advertisers?
Third-party data still has limited uses for broad awareness campaigns where precision is less critical. However, its accuracy has declined as browsers block third-party cookies, and POPIA creates compliance risks for data collected without clear consent. Most SA marketers are prioritising first-party and zero-party data strategies instead.
What is replacing third-party data in digital advertising?
First-party data collected directly from customers, contextual targeting based on page content, zero-party data from explicit preference declarations, and privacy-preserving technologies such as Google's Privacy Sandbox are the main alternatives. Server-side tracking also helps businesses retain measurement accuracy without relying on third-party cookies.
What is the difference between first-party and third-party data?
First-party data is collected directly from your own customers and audience, through your site, purchases and interactions, and you own it. Third-party data is bought from outside aggregators who have no direct relationship with the people it describes. First-party data is more accurate and durable; third-party data is declining.
What is replacing third-party data?
A combination rather than a single successor: first-party data collected directly with consent, contextual targeting based on page content, and privacy-preserving, aggregated measurement. The shift favours owned data and direct relationships over bought, cross-site audience data.