Restaurant chain Wendy's said that the number of restaurants affected by a credit card hack has more than tripled since its initial estimates.

(Image: file photo)

The Columbus, Ohio-based company updated a statement on its website to confirm that 1,025 locations are now thought to have been affected by malware, installed on point-of-sale systems.

It was thought that "fewer than 300" of its 5,144 franchised locations were initially affected when the malware was discovered in May.

The malware was able to obtain cardholder name, card number, expiration date, cardholder verification value, service code, and other data.

The company confirmed the updated details with the California attorney general, which publicly posts data breach notifications on its website.

But the company said that the three or four digit value on the back of the card generally used for online transactions wasn't taken in the breach.

The updated statement said that the list of restaurants affected would be posted online, but wasn't yet available at the time of writing Thursday.