Web Browser Private Modes A Little Leaky

Written by Frank Hayes
August 12th, 2010

In Web browsers, privacy isn’t all it’s cracked up to be. A university study released Wednesday (Aug. 11) says the “privacy mode” available in Internet Explorer, Firefox, Chrome and Safari Web browsers aren’t as secure from prying eyes as users might hope. All four browsers can leak information to some degree, ranging from leaving traces in a PC’s memory to displaying cookies when in private mode, according to a report from the research teams at Stanford and Carnegie Mellon.

The study also points to an interesting project by the Electronic Freedom Foundation (EFF) called Panopticlick, which tries to uniquely identify a user through information the Web browser can’t hide, such as screen resolution, plug-ins, time zone and fonts. The EFF claims it can use that information to identify a browser returning to the site 99 percent of the time, even if it’s in private mode. Fortunately, that still doesn’t expose more information than a cookie.

For retailers, the Stanford/Carnegie Mellon report is a mixed bag. If you had ideas about protecting users from identity theft by encouraging them to use private mode, you may be looking for trouble–any security advice that doesn’t work could be an invitation to a lawsuit. On the other hand, the researchers say that according to their tests, at least 90 percent of users currently don’t use private mode while they’re shopping online. In the case of Microsoft’s Internet Explorer, only 1 percent shop privately.

That may mean users–and their password and payment-card information–are a little less safe than they could be. But it also means the features that private mode usually blocks, including cookies and other customer-tracking techniques, will work fine for the vast majority of retailers.

Most of the information leakage the researchers turned up from the browsers is the sort of thing only forensic detectives would be likely to find: DNS caches not flushed, swap files not cleared, memory not overwritten, SSL certificates preserved. That’s not information available to thieves who don’t have physical access to the users’ PCs.


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