Facebook is in "serious" discussions with Microsoft about a deal to purchase Atlas Solutions, an ad-serving product that Microsoft acquired through its $6 billion acquisition of aQuantive in 2007, according to reports in the technology blogs Business Insider and AllThingsDigital on Thursday.

The deal could allow Facebook to significantly expand its advertising business by showing ads on third-party websites, mounting a challenge to Google Inc's DoubleClick ad network, said the reports, which cited anonymous sources.

The potential price for the acquisition was unclear, though Business Insider said the highest bid for Atlas in Microsoft's previous attempts to sell the business was $30 million.

Facebook and Microsoft representatives declined to comment.

Facebook, the world's No. 1 online social network with roughly 1 billion users, has been moving aggressively to bolster its advertising business with new capabilities, including ads on mobile devices and features that demonstrate the effectiveness of its ads to marketers.

Facebook currently generates 86 percent of its revenue, which totaled roughly $1.3 billion in the third quarter, from ads that appear on its own website.

Shares of Facebook were off 1.2 percent, or 33 cents, at $27.38 in midday trading on Thursday. Microsoft shares were up 7 cents at $26.73.

(Reporting By Alexei Oreskovic; Editing by Neil Stempleman)

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