EXCLUSIVE: Media Buyers Block Publicis’ Epsilon SSP Over Data Leakage Concerns

In the notoriously complex digital advertising supply chain, some brands and their agencies, including a handful of the world’s largest advertising holding companies, have funneled money and data to rival Publicis Groupe without knowing it.

Media buyers fear that by unknowingly purchasing resold publisher inventory—routed through Publicis’ Epsilon-owned supply-side platform (SSP) to other SSPs in open-web auctions—they’ve both funded a competitor and revealed their audience targeting strategies. Epsilon SSP is the only major SSP on the market owned by an agency or holdco.

Over the past 18 months, the media-buying arms of WPP, IPG, Dentsu, and Havas—along with at least four independent agencies and one brand-side programmatic team—purchased ad inventory indirectly through Publicis’ Epsilo