DDG is built on Yahoo BOSS, (Build Your Own Search Service) Yahoo's white-label search engine API. DDG adds spam filtering and some custom indexing on top, but

DDG is built on Yahoo BOSS, (Build Your Own Search Service) Yahoo's white-label search engine API. DDG adds spam filtering and some custom indexing on top, but the bulk of their data comes from Yahoo's index. AFAIK BOSS is still Yahoo technology, not bing. There may be a plan to migrate BOSS to bing.