Building on its slow-but-steady growth over the past few months, Bing saw slight gains again in January in its U.S. search engine share, while Yahoo continued to slide, according to comScore's latest figures.

In December 2011, Microsoft sites -- primarily Bing -- surpassed Yahoo in their share of U.S. searches for the first time, with 15.1 percent versus Yahoo's 14.5 percent.

In January 2012, according to comScore, Microsoft sites had 15.2 percent of U.S. searches, while Yahoo went down to 14.1 percent.

Google went up too in January -- from 65.9 percent in December to 66.2 percent in January.

Here's comScore's chart: