A tweet from billionaire investor Carl Icahn sent Apple Inc. shares up more than five per cent on Tuesday.

Icahn, who earlier this year made a bid to take over Dell, suggested Apple should buy back more stock.

"We currently have a large position in APPLE. We believe the company to be extremely undervalued. Spoke to Tim Cook today. More to come," he wrote in a tweet.


Icahn later revealed he and Cook had talked about Apple’s plan, announced in April, to expand its buyback program to $60 billion US.

"Had a nice conversation with Tim Cook today. Discussed my opinion that a larger buyback should be done now. We plan to speak again shortly," Icahn tweeted.

Icahn, an activist investor who has some 30,000 followers on Twitter, didn’t say how much of a stake he now holds in Apple, but his words had a powerful impact.

Apple shares jumped nearly six per cent to $494.48 US on the news. 

Apple says it plans to return $100 billion US in cash to shareholders by the end of 2015 through dividends and share buybacks.