The owner of a large, illegal offshore sports-betting business was sentenced to 51 months in prison on federal charges, the U.S. Justice Department said.

As part of a plea, Gary Stephen Kaplan, founder of BetOnSports, also agreed to forfeit more than $50 million.

Kaplan pleaded guilty to charges of conspiracy to violate anti-racketeering statutes and the Wire Wager Act and violating the Wire Wager Act, the Justice Department said in a release. The plea agreement was reached in August.

He forfeited $43,650,000 in criminal proceeds to the United States and about $7 million in related proceedings.

In his plea, Kaplan admitted he set up business entities in Aruba, Antigua and Costa Rica to offer sportsbook services to U.S. residents via the Internet and toll-free telephone numbers.

At one point in 2004, BetOnSports had nearly 1 million registered U.S. customers and accepted more than 10 million sports bet that grossed more than $1 billion, the department said. In mid-2004, Kaplan made a successful public offering of the stock of BetOnSports on the London Alternative Investment Market, netting him more than $100 million.

"This case should serve as a warning to others who might choose to defy the laws of the United States on such a grand scale," said Michael W. Reap, acting U.S. attorney. "Kaplan's business model itself was built on a wager that the U.S. could not and would not enforce its anti-sportsbook laws to reach Kaplan. Today, Kaplan lost that wager."