Silicon Valley venture capitalist Marc Andreessen is mocking Warren Buffett for the stock market sage's criticisms of bitcoin, a virtual currency.

Buffett, who has built a $64 billion fortune through his control of Berkshire Hathaway Inc., has dismissed bitcoin as a fad in recent interviews. The putdown irked Andreessen, whose venture capital firm has invested about $50 million in startups betting on bitcoin.

At a bitcoin conference held Tuesday in San Francisco, Andreessen lumped in Buffett among "old white men" who can't grasp new technology.

The 83-year-old Buffett didn't immediately respond to a request for comment.

The 42-year-old Andreessen co-founded Web browser pioneer Netscape. He is also white.

Bitcoin's fate has become a subject of intense debate as the currency's value has swung wildly during the past year.