February 20, 2018

Identifying John Doe: It might be easier than you think

Imagine that you want to sue someone for what they wrote, anonymously, in a web-based online forum. To succeed, you’ll first have to figure out who they really are. How hard is that task? It’s a question that Harlan Yu, Ed Felten, and I have been kicking around for several months. We’ve come to some tentative answers that surprised us, and that may surprise you.

Until recently, I thought the picture was very grim for would-be plaintiffs, writing that it should be simple for “even a non-technical Internet user to engage in effectively untraceable speech online.” I still think it’s feasible for most users, if they make enough effort, to remain anonymous despite any level of scrutiny they are practically likely to face. But in recent months, as Harlan, Ed, and I have discussed this issue, we’ve started to see a flip side to the coin: In many situations, it may be far easier to unmask apparently anonymous online speakers than they, I, or many others in the policy community have appreciated. Today, I’ll tell a story that helps explain what I mean.

Anonymous online speech is a mixed bag: it includes some high value speech such as political dissent in repressive regimes, some dreck we happily tolerate on First Amendment grounds, and some material that violates the laws of many jurisdictions, including child pornography and defamatory speech. For purposes of this discussion, let’s focus on cases like the recent AutoAdmit controversy, in which a plaintiff wishes to bring a defamation suit against an anonymous or pseudonymous poster to a web based discussion forum. I’ll assume, as in the AutoAdmit suit, that the plaintiff has at least a facially plausible legal claim, so that if everyone’s identity were clear, it would also be clear that the plaintiff would have the legal option to bring a defamation suit. In the online context, these are usually what’s called “John Doe” suits, because the plaintiff’s lawyer does not know the name of the defendant in the suit, and must use “John Doe” as a stand in name for the defendant. After filing a John Doe suit, the plaintiff’s lawyer can use subpoenas to force third parties to reveal information that might help identify the John Doe defendant.

In situations like these, if a plaintiff’s lawyer cannot otherwise determine who the poster is, the lawyer will typically subpoena the forum web site, seeking the IP address of the anonymous poster. Many widely used web based discussion systems, including for example the popular WordPress blogging platform, routinely log the IP addresses of commenters. If the web site is able to provide an IP address for the source of the allegedly defamatory comment, the lawyer will do a reverse lookup, a WHOIS search, or both, on that IP address, hoping to discover that the IP address belongs to a residential ISP or another organization that maintains detailed information about its individual users. If the IP address does turn out to correspond to a residential ISP — rather than, say, to an open wifi hub at a coffee shop or library — then the lawyer will issue a second subpoena, asking the ISP to reveal the account details of the user who was using that IP address at the time it was used to transmit the potentially defamatory comment. This is known as a “subpoena chain” because it involves two subpoenas (one to the web site, and a second one, based on the results of the first, to the ISP).

Of course, in many cases, this method won’t work. The forum web site may not have logged the commenter’s IP address. Or, even if an address is available, it might not be readily traceable back to an ISP account: the anonymous commenter may been using an anonymization tool like Tor to hide his address. Or he may have been coming online from a coffee shop or similarly public place (which typically will not have logged information about its transient users). Or, even if he reached the web forum directly from his own ISP, that ISP might be located in a foreign jurisdiction, beyond the reach of an American lawyer’s usual legal tools.

Is this a dead end for the plaintiff’s lawyer, who wants to identify John Doe? Probably not. There are a range of other parties, not yet part of our story, who might have information that could help identify John Doe. When it comes to the AutoAdmit site, one of these parties is StatCounter.com, a web traffic measurement service that AutoAdmit uses to keep track of trends in its traffic over time.

At the moment I am writing this post, anyone can verify that AutoAdmit uses StatCounter by visiting AutoAdmit.com and choosing “View Source” from the web browser menu. The first screenfull of web page code that comes up includes a block of text helpfully labeled “StatCounter Code,” which in turn runs a small piece of javascript that places a personalized StatCounter cookie on the machine of every user who visits AutoAdmit, or else (if one is already present) detects and records exactly which cookie it is. That’s how StatCounter can tell which visitors to AutoAdmit.com are new, which ones are returning, and which pages on the site are of greatest interest to new and returning users. StatCounter is in a position to track not only each user, but also each page, and each visit by a user to a certain page, over time. This includes not only the home page, but also the particular web page for each discussion “thread” on the site. Moreover, each post (even if anonymous) is marked with the time it was posted, down to the minute. So the plaintiff’s lawyer in our story could go to StatCounter, and ask only about visits to the particular thread where the relevant message was posted. If the post went up at 6:03 p.m. on a certain date, the lawyer could ask StatCounter, “What if anything do you know about the person who visited this web page at 6:03 p.m. on this date?” Of course, if John Doe’s browser is configured to refuse cookies, he wouldn’t be trackable. But most web based discussion sites, including AutoAdmit, rely on cookies to let people log in to their pseudonymous accounts in order to post comments in the first place. In any case, the web is much less convenient place without cookies, and as a practical matter most users do allow them.

In fact, the lawyer may be able to do better still: The anonymous commenter will have accessed the page at least twice — once to view the discussion as it stood before he took part, and again after clicking the button to add his own post to the mix. If StatCounter recorded both visits, as it very likely would have, then it becomes even easier to tie the anonymous commenter to his StatCounter cookie (and to whatever browsing history StatCounter has associated with that cookie).

There are a huge number of things to discuss here, and we’ll tackle several in the coming days. What would a web analytics provider like StatCounter know? Likely answers include IP addresses, times, and durations for the anonymous commenter’s previous visits to AutoAdmit. What about other, similar services, used by other sites? What about “beacons” that simply and silently collect data about users, and pay webmasters for the privilege? What about behavioral advertisers, whose business model involves tracking users across multiple sites and developing knowledge of their browsing habits and interests? What about content distribution networks? How would this picture change if John Doe were taking affirmative steps, such as using Tor, to obfuscate his identity?

These are some of the questions that we’ll try to address in future posts.

Anonymization FAIL! Privacy Law FAIL!

I have uploaded my latest draft article entitled, Broken Promises of Privacy: Responding to the Surprising Failure of Anonymization to SSRN (look carefully for the download button, just above the title; it’s a little buried). According to my abstract:

Computer scientists have recently undermined our faith in the privacy-protecting power of anonymization, the name for techniques for protecting the privacy of individuals in large databases by deleting information like names and social security numbers. These scientists have demonstrated they can often “reidentify” or “deanonymize” individuals hidden in anonymized data with astonishing ease. By understanding this research, we will realize we have made a mistake, labored beneath a fundamental misunderstanding, which has assured us much less privacy than we have assumed. This mistake pervades nearly every information privacy law, regulation, and debate, yet regulators and legal scholars have paid it scant attention. We must respond to the surprising failure of anonymization, and this Article provides the tools to do so.

I have labored over this article for a long time, and I am very happy to finally share it publicly. Over the next week, or so, I will write a few blog posts here, summarizing the article’s high points and perhaps expanding on what I couldn’t get to in a mere 28,000 words.

Thanks to Ed, David, and everybody else at Princeton’s CITP for helping me develop this article during my visit earlier this year.

Please let me know what you think, either in these comments or by .