Icahn Drives Apple Stock 5% With a Single Tweet

"We currently have a large position in APPLE," activist investor Carl Icahn tweeted yesterday. "We believe the company to be extremely undervalued. Spoke to Tim Cook today. More to come." That was enough to send Apple stocks soaring up 5%, closing yesterday at $489.57. But Icahn tells the Wall Street Journal that he thinks they should be worth more, and with his "large position"—a sources says it's $1.5 billion worth, though that's probably less than 1%—he's putting the hard word on the tech giant to start buying back shares with its reported $146.6 billion cash stash.

Icahn reckons the company could do a $150 billion buyback now, borrowing at 3%. "If Apple does this now and earnings increase at only 10%, the stock—even keeping the same multiple currently—should trade at $700 a share," he says, per Reuters. Apple confirmed the meeting with CEO Cook, but not whether it would be taking Icahn's advice. As MarketWatch notes, even without the help of Icahn's Twitter feed, the company's stocks have been doing well of late, thanks to an upcoming round of product launches: the new iPhone will be unveiled September 10, and a new thinner, lighter iPad is expected in October. (More Apple stories.)