The Vermont Department of Fish and Wildlife says the department's website was breached and personal information about people who bought licenses online may have been compromised.
The department says there is no conclusive evidence of a misuse of customer information, but experts have found evidence of unauthorized access to servers in 2015 and January 2016.
The state says credit card information is not retained, but in seven cases out of almost 1.7 million transactions, customers entered their credit card numbers into a wrong field, which could have made those numbers subject to theft.
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The department is urging customers who have bought licenses online in the past 14 months to monitor their financial reports for problems.