I know DDG's terms gives it permission to add affiliate links to sites you click on, like Amazon. I can't imagine that funds their operation entirely though.

> Similarly, we may add an affiliate code to some eCommerce sites (e.g. Amazon & eBay) that results in small commissions being paid back to DuckDuckGo when you make purchases at those sites. We do not use any third parties to do the code insertion, and we do not work with any sites that share personally identifiable information (e.g. name, address, etc.) via their affiliate programs.

I read somewhere recently that their revenue is ~1 million annually from ads and affiliate links. I can't remember the source.

Ads are still key.

They make money mainly on ads, based on keyword only (no tracking, ensuring privacy) and affiliate links as mentioned by another commenter.

Keyword based ads are great!