Target Corp. said Monday that the Department of Justice is investigating the credit and debit card security breach at the retailer.

The investigation comes after Target revealed last week that data connected to about 40 million credit and debit card accounts were stolen between Nov. 27 and Dec. 15. Security experts say it's the second-largest theft of card accounts in U.S. history, surpassed only by a scam that began in 2005 involving retailer TJX Cos. That 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.

The news came as Target also said that it is working with the U.S. Secret Service in the retailer's own investigation and that its general counsel held a conference call on Monday with state attorneys general to bring them up to date on the breach.

"Target remains committed to sharing information about the recent data breach with all who are impacted," Molly Snyder, a Target spokeswoman, said in a statement.

Target has been trying to deal with fallout from the breach during what is typically the busiest shopping season of the year. By Monday evening, more than a dozen Target customers had filed federal lawsuits around the country, with some accusing Target of negligence in failing to protect customer data.