Target Corp. said Wednesday that the huge data breach it suffered late last year happened after an intruder stole a vendor's credentials and used them to gain access to the company's computer system.
A Target spokeswoman wouldn't identify the vendor or type of credentials because the retailer is in the midst of forensic and criminal investigations into the malware attack, where cybercrooks hijacked debit and credit card information from up to 110 million people.
"We're conducting an end-to-end review of our systems," spokeswoman Molly Snyder said in an interview.
In a written statement the company issued in response to questions, Snyder said Target has eliminated the malware and closed the access. She said the Minneapolis-based company has also taken extra precautions such as limiting or updating access to some platforms while the investigation continues.
The new detail about stolen credentials sheds a spark of light on a key question that has circled around the heist: How did the cybercrooks break into Target's point-of-sale system to insert malicious software?
Data security blogger Brian Krebs, who first broke the news of Target's breach in December, said he doesn't know with certainty what vendor or stolen credentials Target is referring to.
In his blog, KrebsOnSecurity, Krebs wrote Wednesday that one of the pieces of malware used in the Target attack appeared to be mimicking a default password from an IT management software product used by many major retailers. The software is produced by Houston-based BMC Software, and he suspects Target uses it.
The default password essentially creates a vulnerable back door built into the software.