[frik]

Yahoo "had" plenty of own expertise - they created Hadoop afterall and used it for their own search engine. Until they closed it around 2010 for a deal with Microsoft Bing.

DuckDuckGo uses Yahoo BOSS search API (closed down for everyone but DDG nowadays) which relies on the Bing search engine. https://en.m.wikipedia.org/wiki/Yahoo!_Search_BOSS

If Yahoo hosts the BOSS API on their servers or in on Microsoft servers as part of their deal, isn't known. As DDG recently started to provide the search results from a Yahoo sub-domain (and from Yahoo (or Microsoft?) data centers) to minimize the huge latency (that everyone hates) a little bit.

"To get access to the most relevant Yahoo technology, due to contractual obligations that call has to be associated with a Yahoo domain, in this case, duckduckgo-owned-server.yahoo.net." Of course they mention only the first part, as Yahoo itself relies on the Microsoft contract to access Bing search directly.

See: https://duck.co/help/results/yahoo-technical-implementation and https://en.wikipedia.org/wiki/Yahoo!_Search