Midwestern grocery store Schnucks said over the weekend that its terminals were being used by criminals to capture customers' credit card information at the checkout counter.

The St. Louis company said it hired a computer forensics firm to find the compromised devices. The chain said it's working on determining how many customers were affected and which stores hackers targeted.

"After an extensive review, we confirmed that Schnucks was the victim of a cyberattack," said the company's chairman and chief executive Scott Schnuck, in a press release. "We have identified the issue and taken comprehensive measures to contain the incident. We are cooperating with law enforcement, the Missouri Attorney General's Office, and the credit card companies to determine the scope and magnitude of this crime and apprehend those individuals making fraudulent purchases."

The investigation was originally set off by customer complaints, according to the release.