Sears says Kmart stores targeted in malware attack

Data breach at Kmart

Sears Holdings Corp. said Friday that its Kmart stores were hit with a data breach that compromised some shoppers' debit and credit card information.

The company is working with federal authorities and security experts to investigate the matter. The Secret Service confirmed Friday evening that it is investigating the data breach.

The investigation indicates that the breach occurred in early September and did not affect customers, the statement said.

Read More 10 online retailers going from clicks to bricks

"Based on the forensic investigation to date, no personal information, no debit card PIN numbers, no email addresses and no social security numbers were obtained by those criminally responsible," Sears said in a statement. "We are deploying further advanced software to protect our customers' information."

Sears shares fell about 2 percent in extended-hours trading, after ending the regular session 6 percent lower.

The discount retailer said customers should carefully monitor and review all debit and credit card statements.

Read More 76 Christmas-shopping days left: Are you ready?