Sears Holdings said it was the victim of a cyberattack that likely resulted in the theft of some payment cards at its Kmart stores.

The news marks the latest in a series of computer security breaches to hit U.S. companies and dealing a fresh blow to the struggling company.

The U.S. Secret Service confirmed Friday that it was investigating the breach, which took place last month, and compromised the systems of Kmart.

Kmart has about 1,200 stores across the United States, according to Reuters. Fortunately the breach didn't affect the Sears department store chain.

A Sears spokesman said he couldn't say how many credit and debit card number had taken. The personal information, debit card PIN numbers, email addresses and Social Security numbers of its customers remained safe, the spokesman added.

Security professionals said they weren't surprised to learn of the breach, adding that they believe many big merchants don't have proper systems for detecting cyberattacks.

"This is going to continue indefinitely until people change their practices," said Shawn Henry, a former senior cyber cop with the FBI who is now of the president of cyber forensics firm CrowdStrike Services, according to Reuters.

He added that hackers were able to get into networks because they are "so broad and vast" that attackers will figure out a way in.

Sears said that the attackers used software that was undetectable using anti-virus software. Company spokesman Chris Brathwaite said Sears had been working on upgrading its systems even before the recent spate of incidents involving retailers.

"Our IT team was able to quickly remove the malware and we are deploying further advanced software to protect our customers' information," Brathwaite said.

Tom Kellermann, chief cybersecurity officer with security software maker Trend Micro, said that retailers need to be prepared to deal with malicious software crafted specifically for the purposes of burglarizing retailers.

"It is debatable whether they had sufficient security in place to thwart these thieves," Kellerman said, according to Reuters. "The real question that needs to be asked is why haven't they learned the lessons from the attacks on Target and others."

Kmart apologized to its customers on Friday and added that it was working with security firms, federal authorities and banking partners.

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