Roughly 10 percent of the state population, or 121,000 Hawaii shoppers, were affected by a data breach at Target, one of the nation’s largest retailers.

The retailer notified the public earlier this month that about 40 million credit and debit accounts were compromised by hackers in a data breach at its stores across the country between Nov. 27 and Dec. 15.

Banks and credit unions in the islands have since been on alert, and Target has agreed to free credit report monitoring for one year for all affected cardholders.

Target officials also confirmed Friday that hackers were able to access some personal identification numbers from debit and credit cards used in its stores.

"We are working with Target to ensure that consumers are not held liable for fraudulent purchases," Bruce Kim, executive director of the state Office of Consumer Protection, said Friday in a news release announcing the impact on Hawaii shoppers. "Hawaii consumers who shopped at Target should take precautions to prevent their accounts from being used by monitoring their bank and credit card statements and reporting suspicious activities to their bank or card company. Keep your guard up for the next year because it may take time for any fraudulent transactions to appear."

Target has nearly 1,800 stores in the U.S., with four Hawaii locations — in Hilo and Kona and, on Oahu, in Salt Lake and Kapolei.

Target tried to reassure customers Friday that their PINs were protected by encryption and that the keys to descramble its codes had been stored separately from the systems that had been hacked.

However, security experts said the PINs for the affected cards are vulnerable and people should change their codes because such data has been decrypted, or unlocked, before. PIN data is coveted by cybercriminals because they can make withdrawals from a customer’s account through an ATM.