As many as 40 million credit cards in the United States are at risk for fraud after hackers unleashed a computer virus that stole customer names, bank account numbers and expiration dates from a credit card processing company.

MasterCard International said Friday that about 14 million MasterCards, 20 million Visa cards, and several million American Express and Discover cards could be affected.

High technology thieves, called cybercriminals, try to steal credit card information in order to purchase stolen goods, secure cash advances, or sell account numbers in bulk quantities at underground sites on the Internet.

Under U.S. law, credit card holders who are the victims of fraud are liable for no more than $50 of unauthorized charges.

Industry experts say more than 1 billion credit cards are in use in the United States.

Some information for this report provided by AP and Reuters.