(CBS News) Apple on Tuesday saw its market value spike by about $13 billion after investor, saying that he'd purchased a large chunk of Apple shares because he believes the company's stock could be in much better shape.
Icahn is known for taking big stakes in companies ranging from Yahoo to Motorola and Netflix -- pushing not so subtly for change.
But in an unusual move Tuesday, the 77-year-old revealed his latest venture on Twitter, saying:
We currently have a large position in APPLE. We believe the company to be extremely undervalued. Spoke to Tim Cook today. More to come.— Carl Icahn (@Carl_C_Icahn) August 13, 2013
Cory Johnson, anchor and editor in chief of Bloomberg West, said, "Not through an SEC, Securities and Exchange Commission filing, not through a press release. He used Twitter to get that news out and that instantly sent the stock flying."
Apple's stock price to a near seven-month high -- a boost for a company whose shares have fallen more than 30 percent since last September.
Icahn also tweeted that he talked with Apple chief executive officer Tim Cook to push for a larger stock buyback. Apple's been accused of hoarding too much cash. In a statement, Apple said, "We appreciate the interest and investment of all our shareholders. Tim had a very positive conversation with Mr. Icahn."
Johnson said while Ichan's reported $1.5 billion investment sounds big, it's still very small. "He has less than one percent, probably a quarter of a percentage point worth of Apple's shares. But it's a loud quarter of a percentage point."
The move comes as jittery investors continue to worry about whether Apple can innovate without Steve Jobs. Just Tuesday on "CBS This Morning,"
Asked what happens to Apple without Steve Jobs, Ellison said, "We already know. We conducted the experiment I mean ... it's been done. We saw Apple with Steve Jobs. We saw Apple without Steve Jobs. We saw Apple with Steve Jobs. Now we're gonna see Apple without Steve Jobs."
But now Wall Street, in a different way, is going to see Apple with Carl Icahn.
"Carl Icahn can sometimes change the company in which he makes the investment," Johnson said. "And investors seeing that investment think he might actually change Apple in some important ways."
This is not all Icahn has on his plate right now. He's also used his Twitter account, and his money, to- and their current plans to go private. That battle continues. At 77, Icahn is not exactly slowing down.
Watch Jeff Glor's full report above.