WOODBURY - Target is telling its customers that it is once again safe to use their credit cards.

The retail giant says it has fixed the problem that put 40 million customers at risk, but it won't say exactly how it happened.

The Secret Service stepped in to figure out how credit card and debit card accounts were hacked between Thanksgiving and this week.

Target plans to add more staff to its call centers after reports of people unable to get through yesterday.