Google Inc.’s share of searches in the U.S. market declined in February while that of Microsoft Corp.’s Bing increased, according to research firm ComScore Inc.

Google had 65.4 percent of searches last month, down from 65.6 percent in January, Reston, Virginia-based ComScore said. Microsoft’s Bing search engine had 13.6 percent, up about a half percentage point. Yahoo! Inc.’s share was unchanged at 16.1 percent.

Google, which gets most of its sales from search-engine advertising, is trying to refine the relevance of its results after receiving complaints that some websites game its system to get more prominent placement. Google is rolling out a tool that allows users to hide all listings from sites that they dislike, find offensive or see as low quality, it said in a blog post yesterday.

Last month, Google said it changed the way it carries out Web searches to feature more “high-quality” sites, affecting 12 percent of queries.

Google, based in Mountain View, California, fell $5.17 to $575.13 on the Nasdaq Stock Market at 9:52 a.m. New York time. Microsoft added 5 cents to $25.46.