The investigation comes after the discounter revealed last week that data connected to about 40 million credit and debit card accounts was stolen between November 27 and December 15.
The theft is exceeded only by a scam that began in 2005 involving retailer TJX Cos. It affected at least 45.7 million card users.
The Department of Justice declined to comment on whether it's investigating the breach at Target, the nation's second largest discounter. But Target said that it's cooperating with the DOJ's probe.
"Target remains committed to sharing information about the recent data breach with all who are impacted," said Molly Snyder, a Target spokeswoman, in a statement.
The moves come as Target is trying to deal with the bad publicity that's being generated by the breach during what is typically the busiest shopping season of the year.
By Monday evening, more than a dozen Target customers had already filed class-action lawsuits in federal courts around the country, with some alleging Target was negligent and should have done a better job of protecting customer data.
The company issued an apology to customers and doubled the number of workers taking calls from customers around the clock. It also offered 10 per cent off to customers who wanted to shop in its stores on Saturday and Sunday and free credit-monitoring services to those who are affected by the issue.
But there are early signs that some shoppers are scared off by the breach. Scotty Haywood said he plans to no longer shop at the store because he was a victim of the breach.
"The possible savings of a few dollars (by going to Target) are nothing compared to the money that has been stolen from us," he said.
