Bing took 9.9% of U.S. searches in October, up from 9.4% in September. Google's share rose to 65.4% for the month -- up from 64.9%, sequentially. Growth for Google and Microsoft came at Yahoo's expense, the research firm reported late Monday.

Yahoo slid to 18% in October, from 18.8% in the prior month. Although Broadpoint AmTech Analyst Ben Schachter cautions not to read too much into each data point from comScore, a research note published late Monday reminds investors that Yahoo had ceded share in each of the last nine months, calling it a "worrisome" trend.

"With both Google and Microsoft taking share from Yahoo, it is difficult to pinpoint the reason for the recent share loss acceleration, but Yahoo must find a way to stabilize its share loss or all the effort spent negotiating terms of the search deal will be the least of its worries," Schachter writes.

According to the comScore data, total U.S. searches increased 13.2% in October, below 17.3% growth in September. October also trailed 3Q's 17.3% year-on-year growth.

J.P. Morgan Analyst Imran Khan writes in a published research note that Ask Network's domestic core search market share remained flat at 3.9% from September to October. Ask Network's domestic core search volume rose 4.2% year-on-year, compared with 6.1% growth in September and 4.5% growth in the third quarter, ending in September.

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