SEATTLE – Millions of credit cards may have been exposed to fraud after a security breach at the big discount chains TJ Maxx and Marshalls, but the true extent of the damage is far from being tallied.

Credit card-issuing banks across the country are scrambling to assess and contain the potential for damage to customers' accounts.

It is not clear just how many customers who shopped at both discount stores are affected, but the number could be in the millions.

The parent company of both stores, TJX, says hackers were able to access the portion of the chain's computer network that handles credit card, debit card, check and merchandise return transactions.

The stolen information is from transactions made between May and December of 2006, as well as 2003.

The company says it is cooperating with federal investigators.

For now, TJ Maxx and Marshalls is warning its customers to carefully review their account statements and immediately notify their credit or debit card company or bank if they suspect fraud.

Many shoppers are not terribly surprised.

"I was feeling that could happen to any number of businesses," said one shopper. "That's why I use cash whenever I make a purchase."

In an effort to restore customer confidence, the company says it has shored up its computers, but one retail analyst says it must do more from personal phone calls to discount coupons to lure shoppers back to the stores.

TJ Maxx has set up a toll-free helpline: 866-484-6978.