Mozilla today said it wouldn't -- or couldn't -- pull a "kill switch" to disable the Firesheep add-on that lets anyone steal log-on and account access information to Facebook, Twitter, and other major web services.
Firesheep adds a sidebar to Mozilla's Firefox browser that shows when anyone on an open network -- a coffee shop's Wi-Fi network, for instance -- visits any insecure site on a list that includes the microblogging service Twitter and the hugely-popular Facebook social networking site.
Mozilla has a "blocklist" mechanism that it can, and has in the past, applied as a last-resort defense against potentially-dangerous browser add-ons. The blocklist automatically cripples or uninstalls unwanted extensions that have been added to Firefox.
But Mozilla either can't or won't add Firesheep to the blocklist.
"[Firesheep] demonstrates a security weakness in a number of popular websites, but does not exploit any vulnerability in Firefox or other Web browsers," said Mike Beltzner, director of Firefox, in an e-mail reply to questions about Mozilla's possible moves.
Beltzner did not respond to questions about whether Mozilla is technically able to cripple Firesheep, or simply chooses not to.
As Beltzner pointed out, Firesheep is not an officially-approved Firefox add-on, but was "created and distributed by a third-party developer."
Most Firefox add-ons are obtained by users from the browser's Add-On center , which hosts Mozilla-vetted extensions.
In earlier instances when Mozilla has dealt the blocklist "kill switch" card, it's done so for add-ons that the company had previously approved, but later discovered were stealing information or distributing malware. In July, for example, it yanked a password-stealing extension that had been available from Firefox's gallery for more than a month before its malfeasance was detected.
The add-on, called "Mozilla Sniffer," contained code that intercepted login data submitted to any site, then sent that information to a remote server. Firesheep does some of the same, but it doesn't show what it finds to anyone but the tool's user.
In May 2008, Mozilla acknowledged that a worm had gone unnoticed in Firefox's Vietnamese language add-on for months, and last February it warned users that the Sothink Web Video Downloader 4.0 and all versions of Master Filer were infected with a Trojan horse .
As with Mozilla Sniffer, those add-ons had also been offered in the Firefox add-on center.
Firesheep has proved very popular. Since its Sunday debut, the add-on has been downloaded nearly 320,000 times, or an average of about 79,000 downloads per day. That puts it within striking distance of the Firefox's most popular add-on, Adblock Plus, which has averaged just over 80,000 downloads daily during its lifespan.
Using Firesheep may be a criminal offense under U.S. law, suggested Chet Wisniewski, a senior security adviser at antivirus vendor Sophos. "[Firesheep] isn't illegal, but using this tool is a crime in the U.S.," he said. "It would be considered wiretapping. You can play with it on your own network, use it for research, but not to invade the privacy of others."
While testing the tool, Wisniewski said he was careful only to use it on his own wireless network.
Wisniewski's analysis, however, may be on shaky ground. According to federal wiretapping statutes , it's not a violation of the law "to intercept or access an electronic communication made through an electronic communication system that is configured to that such electronic communication is readily accessible to the general public."