Authorities are committed to hunting down the hackers blamed for a massive data breach at US retail giant Target, Attorney General Eric Holder said Wednesday. Up to 110 million customers had their personal data stolen from the popular store during the year-end holiday shopping season. "The Department of Justice takes seriously reports of any data breach, particularly those involving personally identifiable or financial information, and looks into allegations that are brought to its attention," Holder told lawmakers in Washington. "I can confirm the department is investigating the breach involving the US retailer, Target," he said at a Senate Judiciary Committee hearing. "And we are committed to working to find not only the perpetrators of these sorts of data breaches -- but also any individuals and groups who exploit that data via credit card fraud." Target initially reported on December 19 that hackers had obtained the payment card data of some 40 million customers. On January 10, however, it said its own investigation had revealed that hackers also stole a second batch of data that included names, mailing addresses, phone numbers or email addresses for up to 70 million people. While Target is cooperating with an investigation led by the Justice Department and Secret Service, a group of state attorneys general have launched a parallel investigation aimed at protecting victims. Security researchers have said that the breach is probably linked to a broader global network of cybercrime that may have affected other merchants.