Heartland, a N.J.-based provider of credit and debit card processing services said that unknown intruders had broken into its systems sometime last year and carried on the company's networks. The company, which is among the largest payment processors in the country, claimed to have discovered the intrusion only last week after being alerted by Visa and of suspicious activity.

The card companies' alerts triggered a subsequent investigation by "several forensic investigators" during which the intrusion was discovered, Robert Baldwin Jr., Heartland's president and CFO, said in the statement. The company said the intrusion may have been the result of a "widespread global cyberfraud operation".

Heartland claimed that no merchant data, cardholder's Social Security numbers, or unencrypted personal identification numbers (PIN), addresses or telephone numbers were compromised.

As with most data breach notifications, Heartland offered no explanations on when it was first informed of the breach by the card companies, when in 2008 the company had been breached, how long the intruders had remained undetected, or how many cards might have been compromised in the intrusion. A company spokeswoman did not immediately respond to requests for comment.

But given that Heartland processes more than 100 million card transactions per month, it is very possible that the number of compromised credit and debit cards is at least that much, if not more, said , an analyst with "It does look like the biggest ever," Litan said. The TJX breach involved the compromise of over 45 million cards.