Heartland has yet to disclose the scope of the breach in its systems, saying that it still doesn't know how many card numbers were compromised. The company, which processes more than 100 million transactions per month, also has yet to specify when exactly the system intrusion took place, beyond saying that malware was operational on its systems "during part of 2008."

RBS WorldPay, the Atlanta-based payment processing division of The Royal Bank of Scotland Group, disclosed Dec. 23 that its systems had been breached by unknown intruders, resulting in the compromise of personal information belonging to about 1.5 million owners of prepaid payroll and gift cards (). The compromised information included the of 1.1 million people, according to the company, which said it had discovered the breach in early November.