MINNEAPOLIS (WCCO) — The Grand Casino Mille Lacs says approximately 1,600 card transactions were accessed by an unauthorized person and used for fraudulent transactions.

After finding out on Sept. 15, 2014, the casino says it immediately engaged a leading forensic investigation firm that determined that malware was used to access certain payment card transactions at the Onamia location between April 24 and Oct. 9 of 2014.

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The information accessed includes customer names, payment card numbers and card expiration dates.

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Customers who used cards at the casino between the dates mentioned and see a fraudulent charge on their card should immediately contact their financial institution.

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“Security and privacy are extremely important to Grand Casino Mille Lacs and we deeply regret any inconvenience this may cause. In order to help prevent something like this from occurring again, Grand Casino Mille Lacs continues to work closely with the forensic investigation firm to implement additional security measures,” the casino said in a statement.