Investigators look overseas for hackers in Target case: source WASHINGTON (Reuters) - Investigators believe that overseas hackers were responsible for the cyber attack on U.S. retailer Target Corp that compromised up to 40 million payment cards during the first three weeks of the holiday shopping season, a person familiar with the matter said. The person, who was not authorized to talk publicly about the matter, said that government investigators do not believe that the hackers had inside help. The source declined to say how the hackers got in or where investigators believe they are based, saying investigators don't want to show their hand to the criminals or afford them a chance to destroy evidence. A Secret Service spokesman declined comment on the investigation, which the agency is running. Target spokeswoman Molly Snyder also declined comment. The retailer reported the breach on Thursday, a day after security blogger Brian Krebs broke news of the attack, which was launched as Target entered the busy holiday sales season. The retailer has declined to say how its systems were compromised. Writing by Jim Finkle; Editing by Steve Orlofsky