The Secret Service has confirmed that it is investigating a potential massive data breach involving shoppers' personal credit card information and Target retail stores.

"Approximately 40 million credit and debit card accounts may have been impacted between Nov. 27 and Dec. 15, 2013," Target said Thursday in a statement on it's website.

"The Secret Service will confirm it is investigating the incident at Target," spokesman Brian Leary said in a telephone interview Wednesday night. "We don't have any further comment because it's an ongoing investigation."

The breach involves the theft of information stored on the magnetic stripe on the backs of cards used at nearly all of Target's stores around the country. is the site of Brian Krebs, a national computer security expert and former Washington Post reporter.

Target has almost 1,800 stores in the United States and 124 in Canada, according to its website.

The potential breach does not appear to involve online purchases, Krebs reports. It appears the type of data stolen would allow thieves to create counterfeit credit cards and, if pin numbers were intercepted, would also allow thieves to withdraw cash from ATM machines, according to Krebs.

Getty Images