"We're not trying to make money on short-term moves in Herbalife stock," he said in a "Squawk Box" interview, a day after The Wall Street Journal reported that federal prosecutors and the FBI are investigating potential stock manipulation in regards to Herbalife. According to the Journal, government officials have interviewed people hired by Ackman's $18 billion Pershing Square Capital Management hedge fund.
"Anyone at the government is welcome to look at how we traded this," Ackman said.
He said he knows nothing more about the investigation than what he read in the paper, adding that he has not been contacted directly by the FBI or the Justice Department regarding the matter.
"We've hired a political consultant, a firm called Global Strategy Group. They in turn hire subcontractors around the country and they assisted us in ... advocating on behalf of our very firmly held view that Herbalife is a pyramid scheme," he said. "And my understanding is ... a handful of the people that they've hired or that work for them have been interviewed by the FBI."
Ackman first shorted the nutritional supplement and weight-loss company on May 1, 2012. When he went public with his position in December 2012, the hedge fund manager called the company a pyramid scheme and said his position was worth $1 billion. The company has strongly denied Ackman's charges ever since.
In Friday's CNBC interview, he described his position in Herbalife. "We basically held a large short position in the company that we started in December of 2012 and we've held it up to the stock price rise." He said he changed the form of the position by early 2014 "because we were getting squeezed by Mr. Icahn and others."
Fellow billionaire activist investor Carl Icahn, who famously had a war of words with Ackman on CNBC in 2013, took the other side of Herbalife trade. But last year, the two hugged it out and put aside their past differences at the CNBC-Institutional Investor Delivering Alpha Conference.
"So we covered a bunch of the short, as I've said publicly, and we bought relatively long-dated puts," Ackman said Friday. "What we've done since then is simply rolled those puts and kept on approximately the same size investment."
He said he's spent "something less than $50 million" on his campaign against Herbalife. "The vast majority of that is actually legal fees, and second investigative costs."
Herbalife is a multilevel marketing company that sell products through a network of distributors, many of whom work at home and get paid by selling products, as well as recruiting other distributors. Supporters, including some Latino community leaders, say Herbalife has provided its salespeople with economic opportunity and health benefits.
"Herbalife is a ... criminal enterprise," Ackman said Friday. "It preys on principally undocumented Latino people in the United States and poor around the world. This is a conscious strategy at the most senior management of the company."
Herbalife released a statement to CNBC Thursday night: "Mr. Ackman has a $1 billion bet against Herbalife and a direct financial interest in hurting our company. ... We are confident in the strong fundamentals of our business model and have remained committed to helping people and communities improve their nutrition, while knowing that one day his tactics would be exposed."
CORRECTION: This version corrected the misspelling of Ackman in one reference.