Legendary investor Carl Icahn disclosed on Twitter today that his holding company has taken a 'large position' in Apple, believing that the company is 'extremely undervalued' and should increase its share buyback program. This is similar to the advice that Warren Buffett gave earlier this year, though Buffett did not take a position in Apple. Icahn disclosed his position on Twitter after yesterday warning investors that he may disclose material information on that account in accordance with new SEC guidelines on social media use. Icahn, who has an estimated net worth of $20 billion, has recently been extensively involved in efforts to keep Dell from going private and he also holds a 16% stake in Nuance, the speech recognition company that Apple uses for Siri. Update: According to Bloomberg, Icahn has taken a position of at least $1 billion in Apple and is projecting the stock price to rise to over $600. Update 2: Apple issued this statement regarding Icahn's investment: Update 3: The Wall Street Journal has more from an interview with Mr. Icahn. Article Link: Carl Icahn Discloses 'Large Position' in Apple, Believes Company is 'Extremely Undervalued'