He told CNN he would "go to the end of the earth" to demonstrate this was the case. "If the government comes out and determines this is a completely legal business, then I will lobby Congress for them to change the law. I had a moral obligation. If you knew that Bernie Madoff was running a Ponzi scheme, and you didn't tell anyone about it, and it went on for 33 years ... "
His conviction might have raised a red flag to many investors. But for Mr Icahn, it only made Herbalife sweeter. He showed his disregard for Mr Ackman's judgement by taking a 16pc stake in the business, and becoming its largest investor.
George Soros, founder of Soros Fund Management, also took a susbstantial stake below 5pc, as did Dan Loeb, the founder of Third Point, who was once one of Ackman's close friends.
Mr Loeb has since sold, but he might have benefitted from staying in the game a little longer. So far, Mr Ackman's Pershing Square has lost more than $200m on its bet against Herbalife.
The ongoing brawl with Ackman is not the only battle Mr Icahn has been locked in this year. He has also been engaged in a drawn-out attack on Michael Dell, founder of Dell, who was and is still lobbying to take the computer empire private.
Mr Icahn, who is known for charging into companies and demanding management changes, was unsparing in his criticism. The board's decision to accept Mr Dell's "absurd bargain" was "insulting to shareholders' intelligence", he wrote in an open letter headed "The Great Give Away".
The two billionaires are still slugging it out. Not only are the financial stakes high. Few are in any doubt that Mr Dell will have to walk away from the business that has been his life work if he loses.
More recently, Mr Icahn has invested an estimated $1bn in Apple, and has taken to Twitter to make disclosures about the California technology giant, usually renowned for its secrecy.
Earlier this month he told the public that he was pushing chief executive Tim Cook to increase Apple's buyback plan. Last week he added that he was meeting Mr Cook in September to discuss the size of the return it will make to investors.
Apple, which almost never comments on its strategy outside its financial results, issued a statement welcoming My Icahn's views. No doubt Mr Cook, whose leadership of Apple is already weighed upon by the company's sliding share price and concerns over its pipeline of innovation, wants to keep the hedge fund manager onside.
But some analysts think his new interest in Apple casts a dark cloud over the business."This is absolute trouble," said Patrick Moorhead of Moor Insights & Strategy. "There's not one single positive thing [Apple] can take away from his interest, no matter how much you search."
A bigger share buyback will please shareholders but does not alter the underlying value of the business, analysts claim. Instead they fear that Mr Icahn will destablise a management team that is still struggling to fill the void left by Steve Jobs, Apple's co-founder and former chief executive, who died in 2011.
In some cases, a reshuffle is needed. Mr Loeb ran a successful campaign for change at Yahoo!, ousting not one but two chief executives and the entire board before the company secured its current chief, Marissa Mayer.
Yahoo!'s share price has almost doubled under her tenure and last week the company saw its US web traffic eclipse Google's for the first time in years.
It would be one in the eye for those who are scpetical of activist investors, were it not for the fact that Mr Loeb has now all but abandoned ship. Last month, the New York financier sold two thirds of his 60m share holding in Yahoo! back to the company and resigned from it board, pocketing $520m in the process.
Third Point is now pushing for a break up of Sony. Mr Loeb took an uncharacteristically gentle approach at first, flying to Japan personally to present a letter to the company's chief executive, Kazuo Hirai. In it, he heaped praise upon Mr Hirai's achievements before calling for Sony to consider spinning off part of its entertainment arm of the company to be partly spun off.
Mr Hirai and the rest of the Sony board deliberated over it for several months before coming back with a polite no. It is a slow and subtle stand-off that seems a world away from the aggressive confrontations on Wall Street.
George Clooney, for one, was unconvinced by Mr Loeb's intentions. "He calls himself an activist investor, and I would call him a carpet bagger," he told Deadline, a film industry news website.
"What he's doing is scaring studios and pushing them to make decisions from a place of fear. Why is he buying stock like crazy if he's so down on things? He's trying to manipulate the market."
Although Mr Clooney's expertise are in film, he is right about one thing. Wall Street titans flock to stocks that are undervalued, and try to lobby for changes that can help to propel them upwards.
But that is good for everyone. What is not so good is when the companies in question get caught in the cross fire of other battles: ego driven wars between the billionaires themselves.
