SAN FRANCISCO (Reuters) - Yahoo Inc's board believes Microsoft Corp's unsolicited bid of $44.6 billion to acquire Yahoo "massively undervalues" the company and directors are set to reject the offer, the Wall Street Journal reported on Saturday, citing an unnamed source.

Microsoft's $31 per share offer fails to take account of the risks that a merger between the world's largest software maker and Yahoo would be rejected by regulators, the paper reported, citing "a person familiar with the situation."

A spokeswoman for Yahoo, a diversified Internet media company, declined to comment on the proceedings of the company's board of directors.

(Reporting by Eric Auchard and Anupreeta Das in San Francisco and Megan Davies in New York, editing by Vicki Allen)
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