February 6, 2023

AdNauseam, Google, and the Myth of the “Acceptable Ad”

Earlier this month, we (Helen Nissenbaum, Mushon Zer-Aviv, and I), released a new and improved AdNauseam 3.0. For those not familiar, AdNauseam is the adblocker that clicks every ad in an effort to obfuscate tracking profiles and inject doubt into the lucrative economic system that drives advertising-based surveillance. The 3.0 release contains some new features we’ve been excited to […]

Goodbye, Stanford. Hello, Princeton!

[Editor’s note: The Center for Information Technology Policy (CITP) is delighted to welcome Arvind Narayanan as an Assistant Professor in Computer Science, and an affiliated faculty member in CITP. Narayanan is a leading researcher in digital privacy, data anonymization, and technology policy. His work has been widely published, and includes a paper with CITP co-authors […]

California to Consider Do Not Track Legislation

This afternoon the CA Senate Judiciary Committee had a brief time for proponents and opponents of SB 761 to speak about CA’s Do Not Track legislation. In general, the usual people said the usual things, with a few surprises along the way.

Surprise 1: repeated discussion of privacy as a Constitutional right. For those of us accustomed to privacy at the federal level, it was a good reminder that CA is a little different.

Surprise 2: TechNet compared limits on Internet tracking to Texas banning oil drilling, and claimed DNT is “not necessary” so legislation would be “particularly bad.” Is Kleiner still heavily involved in the post-Wade TechNet?

Surprise 3: the Chamber of Commerce estimated that DNT legislation would cost $4 billion dollars in California, extrapolated from an MIT/Toronto study in the EU. Presumably they mean Goldfarb & Tucker’s Privacy Regulation and Online Advertising, which is in my queue to read. Comments on donottrack.us raise concerns. Assuming even a generous opt-out rate of 5% of CA Internet users, $4B sounds high based on other estimates of value of entire clickstream data for $5/month. I look forward to reading their paper, and to learning the Chamber’s methods of estimating CA based on Europe.

Surprise 4: hearing about the problems of a chilling effect — for job growth, not for online use due to privacy concerns. Similarly, hearing frustrations about a text that says something “might” or “may” happen, with no idea what will actually transpire — about the text of the bill, not about the text of privacy policies.

On a 3 to 2 vote, they sent the bill to the next phase: the Appropriations Committee. Today’s vote was an interesting start.

What are the Constitutional Limits on Online Tracking Regulations?

As the conceptual contours of Do Not Track are being worked out, an interesting question to consider is whether such a regulation—if promulgated—would survive a First Amendment challenge. Could Do Not Track be an unconstitutional restriction on the commercial speech of online tracking entities? The answer would of course depend on what restrictions a potential regulation would specify. However, it may also depend heavily on the outcome of a case currently in front of the Supreme Court—Sorrell v. IMS Health Inc.—that challenges the constitutionality of a Vermont medical privacy law.

The privacy law at issue would restrict pharmacies from selling prescription drug records to data mining companies for marketing purposes without the prescribing doctor’s consent. These drug records each contain extensive details about the doctor-patient relationship, including “the prescriber’s name and address, the name, dosage and quantity of the drug, the date and place the prescription is filled and the patient’s age and gender.” A doctor’s prescription record can be tracked very accurately over time, and while patient names are redacted, each patient is assigned a unique identifier so their prescription histories may also be tracked. Pharmacies have been selling these records to commercial data miners, who in turn aggregate the data and sell compilations to pharmaceutical companies, who then engage in direct marketing back to individual doctors using a practice known as “detailing.” Sound familiar yet? It’s essentially brick-and-mortar behavioral advertising, and a Do Not Track choice mechanism, for prescription drugs.

The Second Circuit recently struck down the Vermont law on First Amendment grounds, ruling first that the law is a regulation of commercial speech and second that the law’s restrictions fall on the wrong side of the Central Hudson test—the four-step analysis used to determine the constitutionality of commercial speech restrictions. This ruling clashes explicitly with two previous decisions in the First Circuit, in Ayotte and Mills, which deemed that similar medical privacy laws in Maine and New Hampshire were constitutional. As such, the Supreme Court decided in January to take the case and resolve the disagreement, and the oral argument is set for April 26th.

I’m not a lawyer, but it seems like the outcome of Sorrell could have a wide-ranging impact on current and future information privacy laws, including possible Do Not Track regulations. Indeed, the petitioners recognize the potentially broad implications of their case. From the petition:

“Information technology has created new and unprecedented opportunities for data mining companies to obtain, monitor, transfer, and use personal information. Indeed, one of the defining traits of the so-called “Information Age” is this ability to amass information about individuals. Computers have made the flow of data concerning everything from personal purchasing habits to real estate records easier to collect than ever before.”

One central question in the case is whether a restriction on access to these data for marketing purposes is a restriction on legitimate commercial speech. The Second Circuit believes it is, reasoning that even “dry information” sold for profit—and already in the hands of a private actor—is entitled to First Amendment protection. In contrast, the First Circuit in Ayotte posited that the information being exchanged has “itself become a commodity,” not unlike beef jerky, so such restrictions are only a limitation on commercial conduct—not speech—and therefore do not implicate any First Amendment concerns.

A major factual difference here, as compared to online privacy and tracking, is that pharmacies are required by many state and federal laws to collect and maintain prescription drug records, so there may be more compelling reasons for the state to restrict access to this information.

In the case of online privacy, it could be argued that Internet users are voluntarily supplying information to the tracking servers, even though many users probably don’t intend to do this, nor do they expect that this is occurring. Judge Livingston, in her circuit dissent in Sorrell, notes that different considerations apply where the government is “prohibiting a speaker from conveying information that the speaker already possesses,” distinguishing that from situations where the government restricts access to the information itself. In applying this to online communications, at what point does the server “possess” the user’s data—when the packets are received and are sitting in a buffer or when the packets are re-assembled and the data permanently stored? Is there a constitutional difference between restrictions on collection versus restrictions on use? The Supreme Court in 1965 in Zemel v. Rusk stated that “the right to speak and publish does not carry with it the unrestrained right to gather information.” To what extent does this apply to government restrictions of online tracking?

The constitutionality of state and federal information privacy laws have historically and consistently been called into question, and things would be no different if—and it’s a big if— Congress grants the FTC authority over online tracking. When considering technical standards and what “tracking” means, it’s worth keeping in mind the possible constitutional challenges insofar as state action may be involved, as some desirable options to curb online tracking may only be possible within a voluntary or self-regulatory framework. Where that line is drawn will depend on how the Supreme Court comes down in Sorrell and how broadly they decide the case.

Some Technical Clarifications About Do Not Track

When I last wrote here about Do Not Track in August, there were just a few rumblings about the possibility of a Do Not Track mechanism for online privacy. Fast forward four months, and Do Not Track has shot to the top of the privacy agenda among regulators in Washington. The FTC staff privacy report released in December endorsed the idea, and Congress was quick to hold a hearing on the issue earlier this month. Now, odds are quite good that some kind of Do Not Track legislation will be introduced early in this new congressional session.

While there isn’t yet a concrete proposal for Do Not Track on the table, much has already been written both in support of and against the idea in general, and it’s terrific to see the issue debated so widely. As I’ve been following along, I’ve noticed some technical confusion on a few points related to Do Not Track, and I’d like to address three of them here.

1. Do Not Track will most likely be based on an HTTP header.

I’ve read some people still suggesting that Do Not Track will be some form of a government-operated list or registry—perhaps of consumer names, device identifiers, tracking domains, or something else. This type of solution has been suggested before in an earlier conception of Do Not Track, and given its rhetorical likeness to the Do Not Call Registry, it’s a natural connection to make. But as I discussed in my earlier post—the details of which I won’t rehash here—a list mechanism is a relatively clumsy solution to this problem for a number of reasons.

A more elegant solution—and the one that many technologists seem to have coalesced around—is the use of a special HTTP header that simply tells the server whether the user is opting out of tracking for that Web request, i.e. the header can be set to either “on” or “off” for each request. If the header is “on,” the server would be responsible for honoring the user’s choice to not be tracked. Users would be able to control this choice through the preferences panel of the browser or the mobile platform.

2. Do Not Track won’t require us to “re-engineer the Internet.”

It’s also been suggested that implementing Do Not Track in this way will require a substantial amount of additional work, possibly even rising to the level of “re-engineering the Internet.” This is decidedly false. The HTTP standard is an extensible one, and it “allows an open-ended set of… headers” to be defined for it. Indeed, custom HTTP headers are used in many Web applications today.

How much work will it take to implement Do Not Track using the header? Generally speaking, not too much. On the client-side, adding the ability to send the Do Not Track header is a relatively simple undertaking. For instance, it only took about 30 minutes of programming to add this functionality to a popular extension for the Firefox Web browser. Other plug-ins already exist. Implementing this functionality directly into the browser might take a little bit longer, but much of the work will be in designing a clear and easily understandable user interface for the option.

On the server-side, adding code to detect the header is also a reasonably easy task—it takes just a few extra lines of code in most popular Web frameworks. It could take more substantial work to program how the server behaves when the header is “on,” but this work is often already necessary even in the absence of Do Not Track. With industry self-regulation, compliant ad servers supposedly already handle the case where a user opts out of their behavioral advertising programs, the difference now being that the opt-out signal comes from a header rather than a cookie. (Of course, the FTC could require stricter standards for what opting-out means.)

Note also that contrary to some suggestions, the header mechanism doesn’t require consumers to identify who they are or otherwise authenticate to servers in order to gain tracking protection. Since the header is a simple on/off flag sent with every Web request, the server doesn’t need to maintain any persistent state about users or their devices’ opt-out preferences.

3. Microsoft’s new Tracking Protection feature isn’t the same as Do Not Track.

Last month, Microsoft announced that its next release of Internet Explorer will include a privacy feature called Tracking Protection. Mozilla is also reportedly considering a similar browser-based solution (although a later report makes it unclear whether they actually will). Browser vendors should be given credit for doing what they can from within their products to protect user privacy, but their efforts are distinct from the Do Not Track header proposal. Let me explain the major difference.

Browser-based features like Tracking Protection basically amount to blocking Web connections from known tracking domains that are compiled on a list. They don’t protect users from tracking by new domains (at least until they’re noticed and added to the tracking list) nor from “allowed” domains that are tracking users surreptitiously.

In contrast, the Do Not Track header compels servers to cooperate, to proactively refrain from any attempts to track the user. The header could be sent to all third-party domains, regardless of whether the domain is already known or whether it actually engages in tracking. With the header, users wouldn’t need to guess whether a domain should be blocked or not, and they wouldn’t have to risk either allowing tracking accidentally or blocking a useful feature.

Tracking Protection and other similar browser-based defenses like Adblock Plus and NoScript are reasonable, but incomplete, interim solutions. They should be viewed as complementary with Do Not Track. For entities under FTC jurisdiction, Do Not Track could put an effective end to the tracking arms race between those entities and browser-based defenses—a race that browsers (and thus consumers) are losing now and will be losing in the foreseeable future. For those entities outside FTC jurisdiction, blocking unwanted third parties is still a useful though leaky defense that maintains the status quo.

Information security experts like to preach “defense in depth” and it’s certainly vital in this case. Neither solution fully protects the user, so users really need both solutions to be available in order to gain more comprehensive protection. As such, the upcoming features in IE and Firefox should not be seen as a technical substitute for Do Not Track.

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To reiterate: if the technology that implements Do Not Track ends up being an HTTP header, which I think it should be, it would be both technically feasible and relatively simple. It’s also distinct from recent browser announcements about privacy in that Do Not Track forces server cooperation, while browser-based defenses work alone to fend off tracking.

What other technical issues related to Do Not Track remain murky to readers? Feel free to leave comments here, or if you prefer on Twitter using the #dntrack tag and @harlanyu.