Mozilla has said that it does not promise to fix critical Firefox vulnerabilities in 10 days after all.

The open source browser maker yesterday retracted a pledge attributed to the company's director of ecosystem development, Mike Schaver, to fix any critical security bugs in the browser within "Ten f***ing Days."

Security researcher Robert Hansen said that Schaver had made the commitment at a late-night pyjama party, hosted by Mozilla at last week's Black Hat conference in Las Vegas.

When Hansen said he doubted that this was possible, Shaver backed up his pledge in writing: putting it on a business card with an arrow linking to his mobile phone number. "I told him I would post his card - and he didn't flinch. No, he wasn't drunk. He's serious," Hansen wrote on his blog.

Mozilla security chief Window Snyder has now offered a refinement to Shaver's late-night scrawl.

"This is not our policy," she wrote in a blog posting. "We do not think security is a game, nor do we issue challenges or ultimatums."

Shaver was trying to explain how responsive the Mozilla team is to bug reports, and not offering a statement of formal policy, Snyder said.

In an interview, Hansen said he never believed that the ten days pledge was official policy.

"What he really wanted to show me was that he believes it's important enough to reach out to the people who are actively finding the vulnerabilities," he said. "There's just no way any company could ever make that claim."

Some vendors ignore independently reported bugs, and frustrated researchers have been known to disclose details for flaws that they feel are taking too long to patch. Mozilla clearly does not want this to happen, and it wants researchers to know it takes these bugs very seriously, Hansen said.

He thinks that Mozilla has done the right thing in making it clear that it does not have a 10-day patch policy, because it's impossible to predict how long it will take to fix all vulnerabilities.

"I think that was the right move," Hansen said. "Mike doesn't have the ability to make that type of policy, especially at a party late at night."