What to Do about Supercookies?
by George Lawton
Ongoing concerns about online privacy have led two members of the US Congress to call for the prohibition of supercookies, which users can't remove from their browsers even with a common delete-cookies command.
These complaints have caused a renewed interest in supercookies.
Representatives Joe Barton and Edward Markey — cochairs of the Congress' Bipartisan Privacy Caucus — wrote the US Federal Trade Commission (FTC) about their concerns.
"I think supercookies should be outlawed because their existence eats away at consumer choice and privacy," argued Baron. "How can you protect yourself from unwanted online tracking of your browsing history when you don’t even know your information is at risk?"
Markey wrote, "Companies should not be … gobbling up personal, sensitive information without users' knowledge. Consumers, not corporations, should have the choice about if, how, or when their personal information is used."
The two Congress members are proposing legislation to help combat supercookies and other online-tracking technologies.
However, some critics are not convinced that legislation banning supercookies is justified.
"I don't think that legislatures or regulators are well positioned to figure out the answers right now," said Jim Harper, a privacy scholar at the Cato Institute, a conservative public-policy research organization.
According to Harper, public pressure, lawsuits, and FTC action based on existing laws will better work out many of the biggest concerns about supercookies.
"And I am hesitant to say that any technology should be banned outright," he noted.
In some cases, Harper explained, tracking users across sites may offer technical benefits such as improving service quality or performance.
"This is just another juncture in a long conversation about what people share when they go online and what kinds of information operators can collect," he said.
Supercookies 101
Cookies — which can work across either single or multiple websites — are useful for storing users' website preferences, shopping-cart items, and so on.
However, they can also store information about what visitors do on the Web across a host site and its partners. Companies can use this information to generate advertisements that target specific users.
A supercookie is a piece of code stored on a computer that collects and regenerates user information after normal cookies have been deleted.
For example, a Flash local stored object lets a website store tracking code on a user's computer. Because it operates as part of the Adobe Systems Flash plug-in, not the browser, it is more difficult for users to control via their browsers' privacy settings. This capability also lets the Flash LSO track users across multiple browsers.
Flash LSOs have grown in usage as Adobe's Flash browser plug-in has increased in popularity.
Another concern is zombie cookies. Individuals who plant these cookies on a victim's site could recreate them even after the recipient deletes them.
When the tracking party places the zombie cookie on a computer, a user ID is stored in the Adobe Flash player storage bin. If the user deletes the cookie, the tracking party can still retrieve the ID and continue collecting information.
Browser fingerprinting identifies users for tracking based on their browser-configuration signatures, IP addresses, plug-ins, system fonts, and operating system.
A website uses a client-side script to collect the data from a visitor's website and store the information in its own database.
ETags: A New Threat
Researchers recently determined that hackers could use entity tags like supercookies.
An ETag is an identifier that a Web server assigns to a specific version of a resource found at a URL. If the content at that URL changes, the Web servers assign it a new ETag.
This lets a system recognize when content hasn't changed between server requests for URL and that the information that browsers have cached is still current. The tags thereby eliminate the need for servers to resend the same information. This makes the process more efficient.
However, the approach also lets online advertisers utilize ETags — which contain information about visitors to sites — as another technique for tracking users.
People who track users via ETags generate unique identifiers that recognize visitors across multiple returns to a given site.
ETags are stored in a browser's cache and aren't eliminated when users delete cookies. Instead, users must manually clear their browser caches to get rid of ETags.
Researchers have already found that some websites are using ETags to track visitors.
A recent US class-action lawsuit — claiming that ETags violate the federal Wiretap Act by tracking Web users in ways that circumvent browser privacy controls — has led some sites to stop employing them.
The War against Supercookies
Several class-action lawsuits against websites using Flash LSOs led to a $3.4 million out-of-court settlement, as well as pledges not to utilize the approach again. Other litigation is pending.
Adobe has updated Flash to make it easier for users to control Flash cookies, noted Seth Schoen, a staff technologist at the Electronic Frontier Foundation, a digital-rights advocacy organization.
The World Wide Web Consortium has launched the Tracking Protection Working Group to improve tracking-control mechanisms.
The group plans to work with browser and search-engine makers, content providers, advertiser networks, and various experts to create standards by mid-2012 that would let users express their tracking preferences and select which parties can track them online.
In addition, major browser makers are experimenting with antitracking approaches.
For example, Microsoft is working with tracking-protection lists, in which users could specify which sites they would let track them.
Mozilla has developed a technique that lets users transmit a do-not-track header to websites.
Google designed the Interface CookieManager API, which makes it easier to filter, edit, preserve, and otherwise handle cookies.
Several other companies have developed improved cookie-management tools for the Chrome browser.
However, Carnegie Mellon University associate professor Lorrie Cranor said she and her research team just finished a study (www.cylab.cmu.edu/files/pdfs/tech_reports/CMUCyLab11017.pdf) of nine tracking-prevention tools and found that they required many manual settings and were difficult for the average consumer to use and configure.
George Lawton is a freelance technology writer based in Guerneville, California. Contact him at glawton@glawton.com.
