Mozilla today said that it regretted staying silent when it found out last week that hackers had stolen digital certificates for some of the Web's biggest sites, including Google, Skype, Microsoft, Yahoo and its own add-on site.

On March 15, attackers used a valid username and password to obtain nine SSL certificates -- which essentially prove that a site is what it says it is -- from an Comodo certificate reseller. The certificates were for six Web sites, including the log-on sites for Microsoft's Hotmail, Google's Gmail, the Internet phone and chat service Skype, and Yahoo Mail. A certificate for Mozilla's Firefox add-on site was also acquired.

Comodo disclosed the breach of its reseller and the theft of the SSL certificates on March 23. Between March 15, when Comodo realized its reseller had been hacked, and March 23, the company revoked the certificates and contacted browser makers Mozilla, Google and Microsoft.

Although Google patched Chrome on March 17, Mozilla and Microsoft issued updates to Firefox and Windows on March 22 and March 23, respectively. Those patches added the stolen certificates to the browsers' blacklists as a fallback defense in case users reached fake sites secured with the certificates.

Comodo said evidence pointed to Iranian government involvement in the attack and theft, and speculated that the certificates were stolen to set up fake sites where authorities could identify activists and monitor their e-mail and other digital communications.

None of the browser makers went public with the Comodo hack or the existence of the rogue certificates before March 22.

"Mozilla did not publish the information we received prior to shipping a patch," the company acknowledged in a Friday entry on its security blog. "In early discussions, we were concerned that any indication that we knew about the attack would lead to attackers blocking our security updates as well."

Today, Mozilla said that that was a mistake.

"In hindsight, while it was made in good faith, this was the wrong decision. We should have informed Web users more quickly about the threat and the potential mitigations as well as their side-effects," said Mozilla.

Jacob Appelbaum, a researcher at the University of Washington's Security and Privacy Research Lab who independently uncovered the certificate theft, had urged Mozilla developers to warn users rather than wait to ship a blacklist update, even if that meant ignoring Comodo's request that everyone stay in sync and not disclose the theft until March 23.

In an interview with Computerworld earlier this week, Appelbaum argued that the delay in disclosing information put Iranian anti-government activists' lives at risk.

"By keeping this quiet for eight days, Comodo and others put lives at risk," charged Appelbaum. "[Iranian activists] were completely unable to protect themselves during that time. Users should have had this information sooner."

And he dismissed the idea that Comodo and the browser makers, particularly Mozilla, should worry about "responsible disclosure" -- the practice of withholding information about a security bug until a fix is ready -- because the underlying problem was not a vulnerability that others could exploit.

"This is not a normal attack. Disclosure does not allow anyone else to perform this attack -- only the attacker with the certificate is able to take advantage of this situation," Appelbaum told Mozilla. "Only the attacker will benefit from a delay."

In a back-and-forth on Bugzilla, the Firefox bug- and change-tracking database, Appelbaum also pushed Mozilla to change the way that Firefox handles OCSP (online certificate status protocol), which is used to determine if a certificate has been revoked by an issuing authority, such as Comodo.

"I really think enabling OCSP to 'required' is the minimum safe thing to do," Appelbaum wrote on Bugzilla March 18, "It's a work around that will fail closed and while it's a bad thing, it seems like the best out of all of a bunch of bad choices."

At times, Appelbaum was scathing in his criticism of Mozilla's refusal to publicly disclose the theft and warn Firefox users.

"Firefox has majorly dropped the ball here," he said Tuesday on Bugzilla. "After the entire CA [certificate authority] model has shown time and time again to be security nightmare, Firefox should have led the way. That's what the Internet expects from Mozilla and it's what I expect from Mozilla."

Appelbaum said some of the same in his interview with Computerworld on Wednesday.

"This was a gigantic failure on Mozilla's part," Appelbaum said then. "They believe disclosure will harm users. That's bogus."

Appelbaum did not reply to an e-mail today requesting comment on Mozilla's mea culpa.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, or subscribe to Gregg's RSS feed . His e-mail address is gkeizer@ix.netcom.com.