New York (CNN Business) As the United States gears up for another presidential election, aware of the role online disinformation played in 2016, the business of publishing false or extremist content online remains a lucrative one.

At least $235 million in revenue is generated annually from ads running on extremist and disinformation websites, according to a new study from the Global Disinformation Index provided exclusively to CNN ahead of its September release. That means the people behind websites propagating hate or false information don't just have an ideological influence — they can also make big money from advertisers who often are unhappy or unaware that their brand name is being displayed alongside content they do not endorse.

The Global Disinformation Index is a nonprofit that assesses websites' risk of spreading disinformation and rates them based on transparency. It defines "disinformation" as inaccurate information spread "purposefully and/or maliciously."

For this latest study, the organization surveyed 20,000 domains it suspected of disinformation, looking at the websites' traffic and audience information, what kinds of ads they were running and how much they made per visitor on advertisements.

The organization's findings reflect just "the tip of the iceberg," Danny Rogers, chief technology officer at the Global Disinformation Index, told CNN's John Avlon on "Reliable Sources" Sunday.