It's sort of a meta search engine that utilizes other search indexes. Here's a post from the founder.

https://duck.co/forum/comment/27893

Edit, that's about 5 years old. The current page on Wikipedia provides a more recent explanation.

"DuckDuckGo's results are a compilation of "about 50" sources,[42] including Yahoo! Search BOSS; Wikipedia; Wolfram Alpha; Bing; its own Web crawler, the DuckDuckBot; and others."

https://en.wikipedia.org/wiki/DuckDuckGo#Overview

They actually say hundreds of sources now on https://duck.co/help/results/sources and specifically call out Bing, Yahoo, and Yandex for search results.

It is a meta search engine. Note that they never mention the share breakdown of these "sources". What percentage of queries DDG itself answer? Probably very few.

Meta-search is a type of search engine that goes way back. They avoid the cost of maintaining a full, search service by sending the query to all kinds of other search engines, running some analysis on their results, and presenting a condensed form to the user optionally with value adds. DuckDuckGo's value add is privacy. Here's some others to give you an idea for what they do:

http://www.searchenginepeople.com/blog/10-meta-search-engine...

Basically DDG is at the mercy of their sources, they can proxy the results for now to the actual search engines, but what happens if lets say Bing and Yandex requires them to pass some extra stuff or cut the query hose otherwise? Will DDG use its own index? Please.. They have no resources to build an actual half decent search engine.

I agree. Being effective and independent will cost money. There some potential for a company that charges monthly or annually to provide search services to other companies with privacy. There's lots of search, like marketing or competitive intelligence, where companies would prefer that the terms don't go through a surveillance company. Initial results might do as DuckDuckGo is doing now with them incrementally building their own database as funds came in.

Not sure how marketable it is, though. Google is pretty dominant. Most companies already running their stuff through it.