October wasn't the best of months for Yahoo search.

According to analysis from Web tracking firm comScore (NASDAQ: SCOR), the Web pioneer seems to caught in the crossfire between Google and Microsoft's Bing.

Google (NASDAQ: GOOG) finished October with 65.4 percent of overall search market share. Bing, by comparison, reached 9.9 percent. Yahoo (NASDAQ: YHOO) meanwhile came in at 18 percent share of U.S. searches.

The trends are revealing. Google's score was up from 64.9 percent in September, while Yahoo's share was its lowest in recent months, down from 18.8 percent in September. Yahoo continued its slide -- in August, its share was at 19.3 percent.

Microsoft's (NASDAQ: MSFT) Bing, meantime, grew from 9.3 percent in August to 9.4 percent in September, and then leaped a half point in October -- so it looks like Yahoo is the one taking a beating.

The downward pressure on Yahoo's search numbers has been evident since at least July, when Bing pulled in 8.9 percent, and Yahoo slipped to 19.4 percent from 19.6 percent.

Even combined, Yahoo and Bing lost share

Yahoo, for its part, has signaled that it's largely throwing in the towel in search, outsourcing it to Microsoft in a deal that will give it a cut of the ad revenue in return.

Until the two giants' search partnership closes, however, the battle between Google and Microsoft continues hurting Yahoo more than each other. And despite Microsoft's efforts to reshape the search landscape with Bing's launch in May and the Yahoo deal, announced in July, comScore's figures suggests that it's Google who's still strong and growing stronger.

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If Microsoft's and Yahoo's deal were to be finalized today -- the agreement is still being hammered out and is being examined by regulators -- the two firms' combined market share would stand at 27.9 percent. That's actually a decrease from September, when they totaled 28.2 percent of the search market.

comScore is not slated to officially release its October numbers until later today, but provides its data to paying clients in advance of publication.