Frost Bank, a subsidiary of Cullen/Frost Bankers, Inc., announced on Friday that it discovered the unauthorized access to images of checks stored electronically.

According to the company, it discovered last week that a third-party lockbox software program had been compromised, resulting in unauthorized users being able to view and copy images of checks stored electronically in the image archive. Frost Bank systems weren’t impacted in the incident, Frost says.

Customers can use lockbox services to send payments to a central post office box. The bank receives the payments and credits them directly to a business’s account.

The information that was accessed as part of the incident could be used to forge checks, the company says.

The company says it stopped the identified unauthorized access immediately after discovering it, and that it also launched an investigation into the matter. Frost says it is working with an unnamed cybersecurity firm to investigate the incident and that the law-enforcement authorities have been informed as well.

“At Frost, we care deeply about taking care of our customers and protecting their information, and we regret that this situation has occurred. We are working very hard to make things right,” Frost Chairman and CEO Phil Green said in a statement.

According to the company, the unauthorized access was limited to a software program serving around 470 commercial customers using the electronic lockbox. The fraction of impacted Frost customer base might experience forgeries on accounts or could be informed of compromised check images.

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Ionut Arghire is an international correspondent for SecurityWeek.

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