The Waterloo Dairy Queen restaurant was among 19 Illinois locations affected by a data breach in August.

Nearly 400 DQ locations nationwide had their software systems compromised, according to news reports.

Dairy Queen said in a statement that its investigation into the breach found evidence that systems were infected with the “Backoff” malware that has already hit a number of U.S. retailers.

A third-party vendor’s compromised account credentials were used to get into the systems at the affected locations, DQ said. Customer names, card numbers and card expiration dates may have been gathered, Dairy Queen said, adding it is confident the malware has now been contained.

The Waterloo store was affected from Aug. 5 to Aug. 31.

Dairy Queen said it was offering one year of free ID repair services from AllClear ID to customers who used a card to pay at one of the impacted locations during the time of this attack.

For a complete list of affected DQ locations, click here.

The Columbia Dairy Queen location was not affected by the data breach.

A request to Waterloo Dairy Queen owner Chad Stultz for comment was not immediately returned.