The Secret Service is investigating a possible data breach at Target stores that may have affected millions of credit and debit cards.
The apparent data breach was first reported Wednesday by security blogger, Brian Krebs, a respected writer on cyber crime and former reporter for the Washington Post.
Krebs said unnamed sources at major credit issuers told him that the security breach started sometime on or near Black Friday. He reported that the breach continued until at least Dec. 6, and that it perhaps continued until as recently as Sunday.
Brian Leary, spokesperson for the Secret Service, said the incident is being investigated, but offered no further details.
A spokesperson for Visa declined to comment. Target representatives did not respond to requests for comment.
Target has 1,797 stores in the U.S. and 124 in Canada.