The Inventory is Dark and Full of Misinformation: Understanding Ad Inventory Pooling in the Ad-Tech Supply Chain

Ad-tech enables publishers to programmatically sell their ad inventory to millions of demand partners through a complex supply chain. The complexity and opacity of the ad-tech supply chain can be exploited by low-quality publishers (e.g., misinformation websites) to deceptively monetize their ad inventory. To combat such deception, the ad-tech industry has developed transparency standards and brand safety products. In this paper, we show that these developments still fall short of preventing deceptive monetization. Specifically, we focus on how publishers can exploit the ad-tech supply chain, subvert ad-tech transparency standards, and undermine brand safety protections by pooling their ad inventory with unrelated sites. This type of deception is referred to as "dark pooling." Our study shows that dark pooling is commonly employed by misinformation publishers on various major ad exchanges, and allows misinformation publishers to deceptively sell their ad inventory to reputable brands. Our work suggests the need for improved vetting of ad exchange supply partners, the adoption of new ad-tech transparency standards that enable end-to-end validation of the ad-tech supply chain, and the widespread deployment of independent audits like ours.