(Bloomberg) — Sears Holdings Corp.'s Kmart discount chain saidit will provide customers with free credit monitoring as itinvestigates a computer-hacker breach detectedlast week.

The retailer's information-technology team identifiedthe breach on Oct. 9 and is working with asecurity firm to assess the incursion, which happened in earlySeptember, Kmart said in an Oct. 10 filing. Customer payment-cardinformation was probably exposed by the attack.

"According to the security experts Kmart has been working with,the Kmart store payment datasystems were infected with aform of malware that was undetectable by current anti-virussystems," the company said in the filing. "Kmart was able toquickly remove the malware. However, Kmart believes certain debitand credit card numbers have been compromised."

A wave of data breaches at companies includingHome Depot Inc., Target Corp. and Neiman Marcus Group Ltd. havepressured retailers to bolster database and credit-card processingsecurity. Nationwide concerns about cyber intrusions have escalatedafter JPMorgan Chase & Co. recently disclosed that an attack byhackers exposed contact information of 76 million households and 7million small businesses.

The company's credit-monitoring offer extends to everyone whoused a credit or debit card at Kmart stores in September throughOct. 9, the company said in an Oct. 10 statement.

Kmart said it doesn't appear that personal information,debit-card PINs, e-mail addresses or social security numbers wereobtained by the hackers. Howard Riefs, a spokesman, was unable toprovide the number of customers affected.

'Advanced Software'

Kmart said in the statement that it's working closely withfederal law enforcement authorities, banking partners and ITsecurity firms in the ongoing investigation and is "deployingfurther advanced software to protect customers' information."

Home Depot's data breach between April andSeptember put about 56 million payment cards at risk, the companysaid in September. The hackers used custom-made software to evadedetection as they infiltrated computers at stores in the U.S. andCanada, relying on tools that haven't been seen in previousattacks, according to the Atlanta-based home improvementretailer.

The company began investigating the attack on Sept. 2,immediately after banking partners and law enforcement raisedalarms that its systems may have been infiltrated. Home Depot hassaid that while payment systems were hacked, there is no evidencethat debit-card PINs have been compromised.

Discount Chain

Target has recorded $146 million in expenses as of Aug. 2related to the discount chain's breach inwhich data for 40 million accounts were stolen.Part of the expenses include an estimate on claims yet to be madeby the credit card companies.

More than 100 lawsuits have been filed against Target relatingto the breach, which contributed to the ouster of ChiefExecutive Officer Gregg Steinhafel in May. The chain also blamedthe attack, which became public in December, for a sales decline inthe fourth quarter.

Hackers also have attacked Supervalu Inc. and AB AcquisitionLLC, the operator of the Albertsons supermarket chain.

Shares of Sears, based in Hoffman Estates, Illinois, fell 6% to$24.78 at the close in New York on Oct. 10, taking its decline forthe year to 38%.

The parent of Kmart is struggling to revive sales growth and isunloading assets to generate cash after nine straight quarters oflosses.

–With assistance from Lauren Coleman-Lochner and MattTownsend in New York and David Wethe in Houston.