The spat between venture capitalist Marc Andreessen and activist investor Carl Icahn took another turn yesterday, with the former accusing the latter of “making up a fake conspiracy theory out of thin air.”

The central event: Microsoft bought Skype in 2011 for $8.5 billion from eBay, which held a minority stake at that point, and from an investment group led by Silver Lake Partners.

Andreessen is a member of the eBay board of directors. His VC firm, Andreessen Horowitz, was part of the Silver Lake-led purchase of 70 percent of Skype from eBay in 2009.

Andreessen Horowitz put up $50 million for that investment when Skype was valued at $2.75 billion, and eBay was left with 30 percent ownership. In less than two years, Skype was sold to Microsoft for $8.5 billion.

In a posting on his company’s blog, Andreessen said Icahn is alleging that Andreessen “improperly usurped [secret information that Microsoft wanted to buy Skype] for my own benefit against the interests of eBay shareholders.”

Icahn’s contention is based on the huge jump in valuation between the two sales. He asserts that eBay undervalued the property when a chunk of it was sold to a board member’s group.

“Don’t tell me that Microsoft suddenly had an epiphany,” Icahn said yesterday on CNBC, “and decided only a year and a half later, ‘Wow, we’re only going to pay $6 billion more.’ ”

Icahn asked if Andreessen had fully briefed the board on Microsoft’s pending interest, which could have raised the valuation. Andreessen and eBay have said that board member Andreessen recused himself from Skype discussions.

The Wall Street Journal noted that Microsoft had discussed a possible purchase with eBay about buying Skype prior to the Silver Lake purchase, according to a court document “and people familiar with the matter.” But Microsoft passed because of pending lawsuits from the Skype founders, who maintained technology ownership. When Microsoft subsequently bought Skype, the lawsuits had been settled.

In addition to this latest accusation, Icahn sent a letter to eBay shareholders recently in which he said Andreessen had advised, and been an investor in, five companies that compete with eBay.

Icahn has been in a running battle to get eBay to spin off its PayPal platform.

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