Wired Magazine reported this week that Wal-Mart kept secret a breach it discovered in November 2006 that had been ongoing for 17 months. According to the article, Walmart claimed there was no reason to disclose the exploit at the time as they believe no customer data or credit card information was breached.
They are admitting that custom developed Point-of-Sale software was breached. The California Breach Law covering breached financial information of California residents had gone into effect on July 1, 2003 and was extended to health information on January 1, 2009. I blogged about that here.
I think it would be more accurate to say that the forensics analysts hired by Wal-Mart could not "prove" that customer data was breached, i.e., could not find specific evidence that customer data was breached. One key piece of information the article revealed, "The company’s server logs recorded only unsuccessful log-in attempts, not successful ones, frustrating a detailed analysis."
Based on my background in log management, I understand the approach of only collecting "bad" events like failed log-ins. Other than this sentence the article does not discuss what types of events were and were not collected. Therefore they have very little idea of what was really going on.
The problem Wal-Mart was facing at the time was that the cost of collecting and storing all the logs in an accessible manner was prohibitive. Fortunately, log data management software has improved and hardware costs have dropped dramatically. In addition there are new tools for user activity monitoring.
However, my key reaction to this article is my disappointment that Wal-Mart chose to keep this incident a secret. It's possible that news of a Wal-Mart breach might have motivated other retailers to strengthen their security defenses and increase their vigilance, which might have reduced the number of breaches that occurred since 2006. It may also have more quickly increased the rigor QSAs applied to PCI DSS audits.
In closing, I would like to call attention to Adam Shostack's and Andrew Stewart's book, "The New School of Information Security," and quote a passage from page 78 which talks about the value of disclosing breaches aside from the need to inform people whose personal financial or health information may have been breached:
"Breach data is bringing us more and better objective data than any past information-sharing initiative in the field of information security. Breach data allows us to see more about the state of computer security than we've been able to with traditional sources of information. … Crucially, breach data allows us to understand what sorts of issues lead to real problems, and this can help us all make better security decisions."