NEW YORK ( TheStreet) -- Apple ( AAPL - Get Report) shares jumped 4% to $486.41 after Carl Icahn announced he has a big stake in the company, calling it "extremely undervalued."

The activist investor noted on Twitter that his firm has a large position in the technology giant. Icahn also noted that he spoke to Apple CEO Tim Cook earlier Tuesday.

Icahn noted that a larger buyback should be done at Apple, and that Icahn and Cook would speak again shortly.

Bloomberg News reported that Icahn's stake in the Cupertino, Calif.-based Apple is worth more than $1 billion.

During Apple's fiscal second-quarter, the company increased its buyback authorization program, adding $50 billion to its buyback program for a total of $100 billion, the largest in U.S. history.

Apple also raised its quarterly dividend to $3.05 per share, an increase of 15% over its previous level.

-- Written by Chris Ciaccia in New York

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