NEW YORK (AP) - Billionaire investor Carl Icahn says Apple should buy back more stock. Icahn said on Twitter Tuesday that he spoke with Apple Inc. CEO Tim Cook and told him the computer company's stock buyback needs to be boosted immediately. Icahn characterized the talk as a "nice conversation" and said he and Cook plan to speak again soon. Apple shares jumped nearly 6 percent to $494.48 on the news. Icahn tweeted that he has a large position in Apple and believes the company's stock is "extremely undervalued." Apple spokesman Steve Dowling confirmed that the two men spoke Tuesday, saying that Cook had a "very positive conversation" with Icahn. Apple said in April that it would expand its stock buyback program to $60 billion, marking the largest buyback authorization in history. The buyback, coupled with an increased dividend, is part of the company's plan to return $100 billion in cash to shareholders by the end of 2015.