A breach of credit and debit card data at discount retailer Target may have affected as many as 40 million shoppers who went to the store in the three weeks after Thanksgiving, the retailer said Thursday.
Late Wednesday, the Secret Service, which is charged with safeguard the nation's financial infrastructure and payment systems, confirmed it was investigating the breach.
Spokesman Brian Leary declined further comment.
The breach first came to light via a report from respected security researcher Brian Krebs that said Target had suffered a data breach around the time of Black Friday last month "potentially involving millions of customer credit and debit card records."
Target, the nation's No. 2 general merchandise retailer after Walmart Stores, said cards used at the brick-and-mortar stores between Nov. 27 and Dec. 15, 2013 may have been impacted.
The retailer said it notified authorities and financial institutions immediately after it was made aware of the unauthorized access, and had hired a forensics team to thoroughly investigate how the breach may have happened.
"Target's first priority is preserving the trust of our guests and we have moved swiftly to address this issue, so guests can shop with confidence," said CEO Gregg Steinhafel in a statement. "We regret any inconvenience this may cause."
The thieves reportedly gained access to data on the magnetic strips of shoppers' cards, potentially allowing them to produce counterfeit versions, according to Krebs.
The thieves could also potentially withdraw cash from ATMs using counterfeit debit cards if they were able to intercept PIN data from Target, he said.
American Express and Discover both said they were "aware" of the incident and had fraud controls in place.
"This is an ongoing investigation," an AmEx spokeswoman said, declining to comment further.
MasterCard referred questions to Target; Visa did not respond to requests for comment.
Target competitor TJX Companies -- which operates discount retail chains T.J. Maxx and Marshalls -- fell victim to one of the worst security breaches ever back in 2006, when hackers gained access to at least 94 million domestic and international accounts containing credit card, debit card, and check information.
Below is the full statement from target.com:
Target today confirmed it is aware of unauthorized access to payment card data that may have impacted certain guests making credit and debit card purchases in its U.S. stores. Target is working closely with law enforcement and financial institutions, and has identified and resolved the issue.
“Target’s first priority is preserving the trust of our guests and we have moved swiftly to address this issue, so guests can shop with confidence. We regret any inconvenience this may cause,” said Gregg Steinhafel, chairman, president and chief executive officer, Target. “We take this matter very seriously and are working with law enforcement to bring those responsible to justice.”
Approximately 40 million credit and debit card accounts may have been impacted between Nov. 27 and Dec. 15, 2013. Target alerted authorities and financial institutions immediately after it was made aware of the unauthorized access, and is putting all appropriate resources behind these efforts. Among other actions, Target is partnering with a leading third-party forensics firm to conduct a thorough investigation of the incident.
More information is available at Target’s corporate website. Guests who suspect unauthorized activity should contact Target at: 866-852-8680.
We also have a link available on the side of the page to Target's corporate website.