BEIJING, Nov. 22 (Xinhunet) -- Market research firm comScore Inc said Google's core web search properties captured 58.5 percent of the U.S. market in October which is the biggest monthly gains, media reported Thursday.

Google attracted 6.1 billion searches of the 10.5 billion searches conducted by U.S. Web users last month. Total search activity grew 12 percent over September, which is typically a slow month until students return to school.

In recent months, comScore introduced an expanded measure of search activity on major Internet sites including not just searches on, for example, Google.com but also searches on other Google properties such as video-sharing site YouTube.

By this measure, Google's Web search activity grew 14.8 percent, or faster than the single-digit growth rates of rivals Yahoo, Microsoft and Time Warner.

Google shares rose more than 3 percent to a high nearing 670 U.S. dollars before settling back later in regular Nasdaq trade to 666.51 dollars, up 2.8 percent.

On Tuesday, broker Credit Suisse set a 900 dollars price target on Google, a new Wall Street high, arguing that the Silicon Valley Internet leader is poised to monopolize search.

"We believe that search is a natural monopoly business and expect that over time Google will continue to gain share until they have effectively reached 100 percent," Credit Suisse analyst Heath Terry wrote in a research note to investors.

(Agencies)