Two New York entrepreneurs, Kevin O’Connor and Dwight Merriman, launched DoubleClick in 1996. Their product, DART, introduced third‑party cookies that let advertisers track users across sites. Google later paid $3.1 billion for the company in 2007, cementing the model that would power the modern web’s ad economy.

DART’s core innovation was the tiny text file set by a server a user never visited, enabling cross‑site profiling. By 1999 DoubleClick merged with data broker Abacus Direct, sparking an FTC probe. The investigation stalled, but the infrastructure survived. Google’s acquisition erased the political hurdle and pushed the architecture into mainstream browsers for advertisers today.

Today a single page averages seven third‑party trackers, and 41.1 % of top‑site traffic carries them. Real‑time bidding pushes roughly 600 billion bid requests per day, or 6.9 million per second. Each tracker adds about 2.5 % to load time, draining bandwidth, battery, and server resources without user consent for publishers and advertisers who depend on data‑driven decisions.

Apple’s App Tracking Transparency (ATT) in 2021 introduced a single OS‑level prompt, setting an opt‑in rate of 15‑25 %. Meta reported a $10 billion revenue dip that year. The experiment showed that a simple user gate can shift billions in ad spend, suggesting browsers could reverse the default without major disruption for the web community today.