"We would like to apologize for this incident and assure our customers that the protection and safekeeping of your information is a responsibility that we take very seriously," the company said in an online posting.
The Toronto Star reported that Honda first noticed suspicious activity on e-commerce Web sites in late February, and that it said in a letter to affected customers dated May 13 that it was tipped off by unusual volume on the sites, including "some unauthorized attempts to access account information."
Honda would not confirm details of the newspaper report.
The company said it is notifying all the affected customers by mail. It said it does not recommend taking any specific action at this time, other than being alert for marketing campaigns from third parties that reference Honda vehicle ownership.
Honda said it has had a toll-free line, (800) 839-2826, open since May 16 for customers who would like further information.
Honda said the data were not the type that typically would be used for identity theft or fraud, such as birth dates, telephone numbers, e-mail addresses, credit card numbers, bank account numbers, driver's license numbers or dollar amounts of financing or payments.
Reuters and Jim Henry contributed to this report