Going ‘Incognito’

Google's slick new browser takes an important step beyond Safari in making stealth browsing easier: When a user opens an "Incognito" tab in Chrome, it not only stops recording history and the words entered into text fields, but also stores all newly-acquired cookies in a temporary folder. As soon as that Incognito tab is closed, its cookies are deleted. That means someone using Google's stealth setting can navigate some normal sites in one tab with all of his or her identifying cookies intact, while simultaneously browsing another set of sites in stealth.

Despite the cookie-killing feature, Google offers no assurances that "Incognito" hides users from advertiser tracking, which could theoretically use tactics other than cookies—the Center for Democracy and Technology, for instance, has observed sites using IP addresses and even downloaded Adobe Flash files to track users. "Incognito is designed to hide your browsing from your computer, not hide it from the Web," says Google engineer Sundar Pichai.

Microsoft's latest version of Internet Explorer has bigger ambitions. IE8 offers both InPrivate Browsing, intended to clean up traces of a user's path from his or her own computer, and InPrivate Blocking, which boasts that it hides the user's behavior from all Web sites that track user identities.

Microsoft's General Manager of Internet Explorer Dean Hachamovitch argues that any element of a site—be it a cookie, an ad or a video—that doesn't come directly from a known site can be used for tracking a user's path around the Web. Once that "third party" object is downloaded to the user's browser, sites can check the user's machine for that file at other visits in his or her Web session. So InPrivate Blocking lets users block all content from third parties or even choose a list of domains whose objects they wish to block.

The result, says Marc Rotenberg, director of the Electronic Privacy Information Center, is the best option for users who want anonymity from advertisers online. "Microsoft is really leading the pack on this issue," he says.

On the more basic concern of cleaning up browsing evidence on a user's own machine, however, Internet Explorer may have missed a more straightforward problem, says Christiane Pickaert, a researcher with Netherlands-based security firm Fox IT. Images and other page elements are still cached in Explorer's temporary Internet files, allowing him to reassemble a user's browsing path piece by piece. In Pickaert's tests, he says, Chrome didn't suffer from the same flaw.