NEW YORK — Citigroup Inc. has started sending replacement credit cards to its customers, apparently in response to a massive security breach at a payment-processing company.

NEW YORK — Citigroup Inc. has started sending replacement credit cards to its customers, apparently in response to a massive security breach at a payment-processing company.

Heartland Payment Systems Inc. revealed on Jan. 20 that its system used to process Visa, MasterCard, American Express and Discover Card transactions was breached late last year.

The Princeton, N.J., company said the breach did not involve merchant data, cardholders' Social Security numbers, unencrypted personal identification numbers, addresses or telephone numbers.

Although a Citi spokeswoman said the bank had no new reports of data breaches since Heartland, she could not immediately confirm if the replacement cards recently sent out were in fact related to the Heartland case. The New York-based bank does not reveal how many of its customers are involved when data security breaches are reported, so it is unclear how many cards were sent out.

Those that were mailed came with a notice labeled "Important Security Message" that explains the "account number may have been illegally obtained as a result of a merchant database compromise and could be at risk for unauthorized use."

Citi has more than 150 million credit card accounts worldwide.

Dozens of banks across the nation have said their customers were involved in the Heartland breach and have issued new cards to consumers. A handful of others have told The Associated Press they are monitoring their systems for unusual activity to detect fraud.

No major new data breaches have been reported to federal officials in recent weeks.

Last year, the number of identity theft cases jumped 22 percent to 9.9 million, according to a study released last week by Javelin Strategy & Research. The fraud price tag totaled $48 million, the study said.

Laws in 44 states require organizations holding consumer data to tell people when their information has leaked, according to the National Conference of State Legislatures.

The Heartland breach is the latest in a series of high-profile breaches for major retailers and banks.