) -- Carl Icahn briefly added over $10 billion in market value to


(AAPL) - Get Report

shares after the billionaire activist

said on Twitter

he has made an investment in the company and views the iPhone maker as "extremely undervalued."

Icahn also noted on Twitter that he spoke to Apple CEO Tim Cook earlier on Tuesday and expects to continue to push for the company to distribute its cash stockpile to investors.

The activist said he spoke with Cook about an increased share buyback. Icahn also said he plans to be in continued communication with Apple.

Apple shares were rising over 4% to $488.30, their highest level since February on the Icahn's Tweet, which came at about 2:21 p.m. ET.

Icahn's Apple comments also come just over a month after he

created a Twitter account


Discussion about Apple is a departure for Icahn, after he has spent the majority of his time on the social network trying to push a competing takeover bid for embattled PC-maker


(DELL) - Get Report


In the second quarter, Apple returned over

$18 billion

to shareholders through dividends and buybacks, after it issued the biggest debt offering in U.S. corporate history.

Apple raised its quarterly dividend to $3.05 per share, an increase of 15% over its previous level. The company's increased shareholder return was largely a result of a somewhat contentious proposal floated by David Einhorn of hedge fund

Greenlight Capital


Einhorn proposed a preferred stock issuance, or what he called iPrefs, in a move that was dismissed by the company. Ultimately, after a court battle and highly publicized conference calls, Apple did increase its return of cash to investors, in a move that Einhorn


he supported.

The hedge funder, however, was not on Twitter to comment on Apple on Tuesday. His last Tweet came in mid-July after bowing out of a poker tournament.


Written by Antoine Gara and Chris Ciaccia in New York

Follow @antoinegara