Carl Icahn tweets about large stake in Apple, chat with CEO

Activist investor Carl Icahn has an eye on Apple.

Icahn took to Twitter on Tuesday, where he had so far only sent out 10 tweets since June, to note that his investment group had a "large position in Apple," and that he believed the company to be "extremely undervalued."

Icahn also noted that he had a "nice conversation" with Apple CEO Tim Cook, where he made the case the company should do a larger repurchasing of shares, beyond its current plan. That plan, which is scheduled to run through the end of 2015, involves the repurchasing of $60 billion in Apple shares.

So far there's no indication of just how much of a position Icahn actually has with the company, but it was enough to send shares of Apple up $22.21, or 4.75 percent, to close at $489.57.

In a statement given to AllThingsD, Apple said it appreciated "the interest and investment of all our shareholders," and that "Tim (Cook) had a very positive conversation with Mr. Icahn today."

Icahn's investment is notable given a history of getting involved with the companies he takes interest in. That includes waging proxy fights, or threatening to do so with companies like Yahoo, Motorola, Time Warner, Blockbuster, ImClone Systems, and nearly Netflix. More recently that list has included Dell, where Icahn has filed a lawsuit against the company and its board to keep Dell from going private.

The tweets come just a day after Icahn's investment group, Icahn Enterprises noted that he would be using the account to note "material" information:

Our Chairman, Carl C. Icahn, intends to use Twitter from time to time to communicate with the public about our company and other issues. Mr. Icahn's Twitter handle is @Carl_C_Icahn. It is possible that the information that Mr. Icahn posts on Twitter (which may include information regarding companies in which we and/or Mr. Icahn have or may be contemplating an investment position) could be deemed to be material information.

Icahn joined the social network in late June, posting his first tweet on June 20 -- ribbing Dell by saying "Twitter is great. I like it almost as much as I like Dell." Just ahead of the pair of Apple tweets, Icahn only posted nine other tweets, primarily around his fight against Dell, but also tweets about celebrating the Fourth of July, an appearance at the Delivering Alpha Conference, and a story he contributed to Forbes.

Update at 1 p.m. PT to include Apple's closing stock price, as well as more background on Icahn joining Twitter.