Forty million Target credit and debit card accounts were stolen from Nov. 27 and Dec. 15 The Wall Street Journal reported Thursday.
The information taken included Customer names, credit or debit card numbers, expiration dates, and CVV security codes were taken. Law enforcement and banks were notified directly after the incident occurred.
Target employees found and solved where the problem was coming from, but were not able to locate the person behind the incident, and the way they went about it.
"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," Gregg Steinhafel, CEO at Target told Bloomberg Businessweek. "We take this matter very seriously and are working with law enforcement to bring those responsible to justice.
The incident spanned the country in Target stores, and not online, and could have involved thieves fiddling with the machines customers utilize to slide their cards through while purchasing merchandise Bloomberg Businessweek reported.
"This was obviously a very sophisticated crime," said Molly Snyder, a Target spokeswoman told The Journal.
The retailer is working with a forensic's firm to look for answers to why the incident happened. The Secret Service is also looking into the matter.
"While this search for the truth is happening, the issue damages the trust Target have gained in mobile and calls into question how sales (will) trend in January," Brian Sozzi, CEO at Belus Capital Advisors told Reuters.
There are 1,797 Target stores in the United States. The retailer also has 124 in Canada.
The retailer's shares decreased 1.3 percent to $62.72 Thursday morning. Numbers also showed a 7.4 increase in 2013 before Wednesday.
Sales in the retail business went up two percent last week because of an influx in customers for the holiday shopping season.
