PHOENIX -- Arizona Central Credit Union has sent letters to approximately 12,000 customers whose check card numbers may have been compromised.

David Kexel, vice president of marketing and business development for Arizona Central Credit Union, said there was a data breach at a merchant card processor. Those are the companies that process card transactions at stores and restaurants.

Arizona Central Credit Union realized that some of its customers did business at the stores and restaurants that used the merchant card processor. It has sent those customers a letter, letting them know that the check card numbers may have been compromised.

It is also canceling the cards and replacing them with new ones.

"We are doing everything we can to protect their accounts," Kexel said. "We didn't have much control over what happened."

Kexel stressed that it was not Arizona Central Credit Union's processors that suffered the data breach. He also stressed that Arizona Central Credit Union was not the only financial institution affected by the data breach.

He added that the company also has a monitoring system already in place that monitors accounts and red flags the company when there is strange activity.

Todd Davis, CEO of the identity theft company LifeLock, said Arizona Central Credit Union made the right decision by alerting the customers to what happened and canceling the cards.

He adds that all people would be wise to put fraud alerts on their accounts, check their monthly statements for irregularities as soon as they arrive and order credit reports.

"Go be proactive to protect yourself. Assume your information is going to get into the wrong hands," Davis said. "You can get on top of it quickly. Find something. Detect the problem as early as you can."

Davis said the worst-case scenario would be if someone had access to your information and opened up a new credit card in your name. He said it would be a lengthy process to rectify that situation.