Yahoo saw its search business lose more ground against rivals Google and Microsoft last month.
A recent report from traffic monitoring firm comScore estimated that Yahoo's total share of all US search queries fell by 0.5 per cent on the month to 17.5 per cent.
Microsoft increased its share from 9.9 to 10.3 per cent, while Google saw a 0.2 per cent increase to 65.6 per cent.
Overall, Yahoo also saw its search engine traffic drop by two per cent on the month, while Bing grew by six per cent and Google by one per cent.
Microsoft's Bing logged an estimated 1.5 billion search queries, while Yahoo handled 2.6 billion and Google 13.8 billion.
The results will be a setback for Yahoo, which has spent the year trying to remake its image and win a greater share of the search market under new chief executive Carol Bartz.
Yahoo's loss continues to be Microsoft's gain. Bing was launched in June, and has consistently gained ground on its two larger rivals, mostly at the expense of Yahoo.
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