Target says it's fixed the problem that allowed credit and debit card information on as many as 40 million accounts to be stolen.
The chain, however, recommends customers should check their statements carefully for unauthorized charges.
The accounts at risk are those of customers who swiped their cards at stores in the U.S. between November 27 and December 15.
The breach didn't affect online purchases. The stolen information included Target store brand cards and major card brands such as Visa and MasterCard.
News 2 spoke with a computer security expert Dr. Fred Scholl at Lipscomb University Thursday who said there wasn't anything shoppers could have done to protect themselves.
He said he puts the blame on the company.
“They fail to monitor their own systems, they may put in security software and hardware controls, but it's monitoring the daily activity of their systems to detect things like this,” Scholl said.
“It's like, you set up security cameras looking for people breaking onto your property, the question is anyone looking at these security cameras,” he said.
Despite the problem being fixed, customers may not be out of the woods yet.
According to Dr. Scholl, items charged to a person's credit card account could take weeks to show up on their statement.
Computer experts say the breach may have occurred after an employee clicked on a malicious Web site link that installed malware on Target computers.
“They'll send them some type of targeted e-mail that's spoofed to come from a bank or the IRS or even another Target employee,” Scholl explained.
He continued, “They click on that link and even if they have second thoughts, it's too late the software can get installed on their machine then it can go out browsing the Target network, looking for weak-spots where they can get this type of information.”
Scholl suggests that Tennessee customers contact state lawmakers and encourage them to pass a computer security bill that would protect consumers.
Customers who see suspicious activity in their accounts are being told to call Target at 866-852-8680. Target has 1,797 U.S. stores and 124 in Canada.
The retailer's stock dipped about two percent in Thursday morning's trading.
*The Associated Press contributed to this report.