But the Yahoo breach is having a ripple effect through the industry. That's because the passwords to the 453,492 accounts not only belong to Yahoo users, they also work on Gmail, Hotmail, AOL, MSN, Comcast, SBC Global, Bellsouth, Live.com and Verizon accounts.

In a published statement, Yahoo said it was "fixing the vulnerability that led to the disclosure of this data , changing the passwords of the affected Yahoo users and notifying companies whose user accounts may have been compromised." But security experts are still suggesting users change their passwords to Yahoo and other sites.

A Black Market for Passwords

We turned to Chris Petersen, chief technology officer and founder of LogRhythm, to get his second-day reaction on the Yahoo breach. He told us Web applications continue to be seen as a soft target by cyber criminals looking to sell passwords on the black market.

"Passwords are of value when associated with an e-mail account, which is purported to be the case in the Yahoo breach," Petersen said. "Because users often use the same password across different accounts, cyber criminals might be able to access other sites, company networks, and banking accounts if they can successfully map the compromised e-mail address to the individual that owns it."

Petersen is charging organizations to start doing a better job of implementing Web application defenses if they want to avoid being the next Yahoo. Perimeter defenses including Web application firewalls are a good start but by themselves not sufficient.

"These technologies operate largely on the premise they can detect what is known," Petersen said. "To have a chance detecting what is not known, additional monitoring and response approaches must be employed. For example, by analyzing Web server logs and network activity patterns, attacks that evade perimeter defense can still be detected and defended against."

Detecting Hackers

Tom Cross, director of security research at Lancope, said there are a lot of passwords and password hashes circulating in the underground after a string of recent breaches and disclosures like this one and the recent LinkedIn hack that saw 6.5 million passwords exposed on a Russian site.

"We have every reason to believe that we are going to see similar compromises in the future," Cross told us. "These passwords are going to be used to compromise corporate networks."

From Cross' perspective, the question that we need to be asking is this: How do we detect attackers who log into our networks with legitimate credentials?

"Organizations that are only focused on looking for exploit activity at the network perimeter can't see attacks after they've already gotten in the front door," Cross said. "IT security teams also need visibility into authorized traffic on the internal network that enables them to detect and mitigate compromises after the walls have been breached."