The switched occurred Wednesday but was announced last month as part of an expanded deal between CNN.com and Yahoo subsidiary Overture Services Inc., which provides search-based advertising.
Overture already has been providing paid search results for CNN.com. As part of the new agreement, it has added contextual ads, triggered by a Web pages content, to the mix.
The switch marks one of the biggest made public since Yahoo revamped its search technology in February and dropped Google for results on its Web portal, the most visited network of sites in the United States.
Yahoo executives were holding their annual analysts day Thursday in San Francisco, where CEO Terry Semel assured analysts that Yahoo is ready for the increased competition, according to the Associated Press. Officials at the Sunnyvale, Calif., company were not available for comment on the CNN.com switch.
CNN.com, of Atlanta, is a unit of Time Warner Inc., which is also the parent company of America Online Inc. Ironically, AOL last year renewed its partnership with Google for both its Web search results and its search-based ads.
The switch to Yahoo Search reaches across CNN.coms network of sites, including those for Sports Illustrated and CNN/Money. The sites now display a search query box that says "Powered by Yahoo Search."