In an email sent Monday afternoon to all Microsoft employees, Satya Nadella, senior vice president of research and development for Microsoft's online services division, invited company staffers to begin testing the Kumo search engine, currently only available on the company's internal network. For now, Microsoft's Live Search, at, remains the company's search engine for the public.

A person familiar with the matter said Microsoft hasn't decided yet whether to rebrand Live Search as Kumo, which Mr. Nadella refers to as a code name in his email. Kumo in Japanese means spider, a reference to so-called spider software that crawls from Web site to Web site, adding the data to vast search-engine indexes.

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