Bing's gains came from Yahoo, which dropped from 17 percent through January to 16.8 percent in February, according to research from comScore released March 9. Google grew slightly in February, notching 65.5 percent, up from 65.4 percent from the prior month.

The big story here is the rise of Bing and the corresponding plunge of Yahoo. Since its June 2009 launch, Bing has tacked on 350 basis points of growth, while Yahoo has lost roughly 330 basis points since May 2009, according to Jefferies & Co. analyst Youssef Squali.

It is unlikely that Yahoo will recover to post any significant growth, given the commencement of its search deal to let Bing power its search results for the next decade.

Squali sees the $100 million advertising and marketing campaign as a big reason, along with the Bing Cashback program, unique user interface and focus on industry verticals, such as travel and shopping.

FBR Capital Markets meanwhile said much of Microsoft's share gains can be attributed to the addition of trending search queries on MSN and the company's aggressive ad campaign for Bing. The continuation of this campaign could translate well overseas.