Chase Had Ads on 400,000 Sites. Then on Just 5,000. Same Results. - The New York Times

Tangentially, see Why the YouTube Ad Boycott Could Cost Google $750 Million (Fortune)

"The change illustrates the new skepticism with which major marketers are approaching online ad platforms and the automated technology placing their brands on millions of websites. In recent years, advertisers have increasingly shunned buying ads on individual sites in favor of cheaply targeting groups of people across the web based on their browsing habits, a process known as programmatic advertising — enabling, say, a Gerber ad to show up on a local mother’s blog, or a purse in an online shopping cart to follow a person around the internet for weeks.

But as the risks around the far reaches of the web have been cast into stark relief, some advertisers are questioning the value of showing up on hundreds of thousands of unknown sites, and wondering whether millions of appearances actually translate into more sales."

Chase Had Ads on 400,000 Sites. Then on Just 5,000. Same Results. - The New York Times