Leading the pack is Heartland Payment Systems(HPY). The company processes credit card payments, so naturally, it was a huge target. It was hacked in 2008, losing data on 130 million customers.
Heartland eventually paid more than $110 million to Visa(V), MasterCard(MA), American Express(AXP) and other card associations to settle claims related to the breach.
Numbers gathered by DataLossDB shows that no other data breach is even close.