A New England-based supermarket, Hannaford Bros., said Monday that a system breach may have given criminals access to more than 4 million credit and debit cards. It's a significant event, and while the facts aren't out yet, it looks unlike most other breaches.This breach, which was covered here by CRN and earlier today by my colleague Andrew Conry-Murray, is liable to start a big debate over the voracity of PCI DSS. As Conry-Murray points out, while Hannaford Bros. was breached, it's also in compliance with PCI DSS.

In several discussions today and e-mails I received, some are starting to point out that Hannaford Bros. was breached even though the retailer appears to have been compliant with PCI DSS.

What surprised me during these discussions is that some folks seemed so surprised that a retailer that is PCI compliant could be successfully breached.

These standards don't guarantee 100% security, or 99% security ... or any percentage of security, for that matter. What compliance does show is that the retailer had proper security controls in place to mitigate the risks of attack -- not eliminate them.

What makes this attack interesting is that it appears (we don't have all of the facts yet) that the credit card information was pilfered while the cards were being authorized for payment. Perhaps it was another insecure wireless network, such as was the case with the TJX hack, or maybe someone was able to slip a network sniffer somewhere on the inside.

If it turns out that the data was stolen while in transit, and that data was not encrypted, there's a hole in the PCI DSS standard that needs to be filled.

While getting to the bottom of how the breach occurred won't help the 1,800 customers who already have experienced fraudulent activity on their accounts, it may help prevent it from happening again.