Officials with the retail giant Target have responded to the nationwide credit and debit card data theft that may affect as many as 40 million accounts.

Target tweeted Thursday that 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.

Tamara Herz thinks she was one of the victims. 

“I said how could has this happened? What is going on?” she said.

Just recently, she noticed fraudulent purchases made with her bank card. She said it's the same card she used while shopping at Target this holiday. 

“Now I know where my cards was compromised, most likely,” she said.

Officials said via twitter that Target is working closely with law enforcement and financial institutions, and has identified and resolved the issue. The Secret Service is investigating.

“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.”

Officials said about 40 million credit and debit card accounts may have been affected by a data breach.

The chain said Thursday that the accounts may have been impacted between Nov. 27 and Dec. 15.

The Minneapolis company said it immediately told authorities and financial institutions once it became aware of the breach and that it is teaming with a third-party forensics firm to investigate the matter.

Target Corp. said that customers who made purchases at its U.S. stores during the impacted period and suspected unauthorized activity should call them at 866-852-8680.

Target has 1,797 U.S. stores and 124 in Canada.