Billionaire investor Carl Icahn used Twitter on Tuesday to reveal that he has a large amount of Apple stock, and that he believes the company to be "extremely undervalued." The tweet, and a follow-up about discussing share buybacks with Apple CEO Tim Cook, sent Apple's price soaring, boosting the company's value by about $20 billion. "I don't know that market-moving information breaking on Twitter will become 'the norm,' but it has certainly become important," said Henry Blodget, CEO of Business Insider.

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