DDG has its own index, you get offered bing/google when there is too few results...

NolF on Sept 17, 2012 | parent | context | favorite | on: Facebook’s embedded option

DDG has its own index, you get offered bing/google when there is too few results from DDG. Even when you click bing/google, it is anonymized, so the results are not skewed by the info the search engines have on you.