A spokesman of the firm, Paddy Power, confirmed the incident Friday, but referred questions to an earlier statement on the "historic breach."
The firm's statement on July 31 said it was "advised" of the incident in May, and a Canadian had the data, which was recovered with the help of the Ontario Provincial Police.
"Paddy Power sought and received two court orders in Canada to seize the individual’s IT (information technology) assets... to examine his bank accounts and financial transactions and to question him," it said.
"The court orders were secured and executed in Canada during the week of July 7."
Neither Paddy Power nor police named the Canadian in question.
The OPP said officers assisted in the matter, but its involvement in the matter has ended. It added police haven't laid charges, though it did not elaborate on the reason.
It was not immediately known how the Canadian came into possession of the data.
Paddy Power said the data was stolen during a "cyber attack" in 2010, and therefore does not affect customers who signed up after that year.
It added data involved did not include financial information or passwords, but did include names, usernames, addresses, email addresses, phone numbers, date of birth and security questions and answers.
"Paddy Power’s account monitoring has not detected any suspicious activity to indicate that customers’ accounts have been adversely impacted in any way," the firm said.
The firm is asking affected customers to review other sites where they use the same security questions and answers, and to "update where appropriate."
Paddy Power managing director Peter O'Donovan said in a statement the firm regrets the breach and apologizes to "people who have been inconvenienced as a result.”
The firm is known for sometimes offering unusual bets, such as on a potential assassination of U.S. President Barack Obama and the Toronto mayoral election.