Facebook has estimated it was not worth anything near the $15bn market value implied when Microsoft took a stake in the firm in 2007.
Court documents that were used in a legal dispute last year, show Facebook's own appraisal had priced its privately held stock at $8.88. This would give the firm a market value of about $3.7bn.
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The company relied on the value appraisal to value employee stock options fairly and avoid possible tax problems.
Facebook made the estimate after signing an October 2007 advertising deal with Microsoft, which saw Redmond take a 1.6% stake in Facebook for $240m.
The Microsoft investment had implied Facebook's stock was worth $35.90 per share. This figure was used in the settlement of a lawsuit last year that had accused the company's founder Mark Zuckerberg of stealing the idea for his online service from three former college classmates who started rival social network ConnectU.
Facebook had attempted to keep the figures used by both sides in the dispute private, but Associated Press obtained them after copying blacked-out portions of an electronic document and pasting the results into another document.
Under the settlement, Facebook agreed to pay ConnectU $20m in cash and 1,253,326 shares of common stock. The stock was worth $45m based on the Microsoft valuation, but only $11m under Facebook's own appraisal.
That means ConnectU received anywhere from $31m and $65m for settling the suit, depending on which stock valuation is used.