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Web Browser Weaknesses Make Tracking Easy

Researcher kicks off effort to catalog all the ways that browsers and popular add-ons can be used to track users

While users generally do not like the idea of being tracked as they browse online, there are any number of legitimate reasons for tracking visitors to your Web site: counting unique users, tracking browsing behavior, and even security.

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Companies that are interested in monitoring the comings and goings of potentially bad actors can also benefit from better tracking techniques. At the Black Hat conference in Las Vegas, senior security consultant Gregory Fleischer of FishNet Security cataloged the ways that companies can fingerprint visitors' browsers and systems, track their visits, and further unmask their identities.

Echoing Sun Microsystems CEO Scott McNealy's infamous comment from 1999 -- "You have zero privacy anyway, get over it." -- Fleischer told attendees not to expect websites to give up tracking users.

"Web tracking is inevitable -- it is going to happen, and it's here to stay," he said. "It will be more pervasive in the future."

Many of the design decisions used to increase browser functionality also allow sites to more persistently track their visitors. Tracking makes uses of information leaked by a browser, either because of a design weakness or just as an offshoot of the browser's normal functionality.

"Ultimately, an effective tracking solution needs to encompass all facets of information exposed by the browser, but care should be taken to avoid relying on user cooperation, deception, or outright theft of user information," Fleischer stated in his whitepaper on the topic.

[ A security research group uses cached JavaScript to control computers connecting to a malicious proxy, gaining intelligence on fraudsters and criminals. See JavaScript Botnet Sheds Light On Criminal Activity. ]

Fingerprinting allows the tracker to keep tabs on a user, even when he may take actions to foil the eavesdropping. In particular, the plug-ins installed by a user can help websites create a better fingerprint of the user's system. For example, the existence of NoScript, a popular Firefox plug-in that blocks unwanted Javascript from running, can be detected and become a component in a robust fingerprint, Fleischer said.

Because plug-ins offer more detailed access to machine-specific and software-specific characteristics, they can create better fingerprints of systems and help track visitors more reliably. Ubiquitous plug-ins -- such as Adobe Flash and Acrobat, Microsoft Silverlight, and Oracle's Java -- can all reveal system data that can identify a system. Java, in particular, can be used to collect information that can make up a more reliable fingerprint.

"When you have Java installed, it is very easy to set an ID," he said.

Fingerprinting can track visitors even if they use anonymizing technologies, such as proxy servers and the Tor network. Other privacy technologies can be easily circumvented to allow tracking, according to Fleischer. Private browsing modes, for example, can be evaded, especially by coordination between sites. And tracking protection lists, a blacklisting technology to block bad actors, are not foolproof either, he said.

Finally, sites that work together can correlate their tracking information to better track visitors.

"By correlating over time and over large networks, sites that are tracking will have better results," he said.

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