Online Trackers Follow Our Digital Shadow By 'Fingerprinting' Browsers, Devices

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New technology helps trackers follow consumers' digital imprints — including across devices — through browser settings, battery levels and other details.

As we surf from website to website, we are being tracked — that's not news. What is news, revealed in a recent paper by researchers at Princeton University, is that the tracking is no longer just about the "cookies" that record our tastes. The researchers surveyed a million websites and found that state-of-the-art tracking is a lot more sophisticated, allowing websites to track the fingerprints left by our devices.

Princeton's Arvind Narayanan and Steven Englehardt studied how all the things we do not see as users are valuable to someone on our digital trail, as our presence may be authenticated and tracked through such minutia as personalized browser settings or even our laptops' battery levels.

Fingerprinting "allows a tracker to put an identifier on your entire history of online activity," Narayanan, assistant professor of computer science, tells NPR's Robert Siegel. "They've been collecting those histories, that's not new — that's a given. But what the technological sophistication is for, is for linking all of your online breadcrumbs together, even if you're not necessarily putting your real name or email address into all your online interactions."

Interview Highlights

On how fingerprinting techniques work

It turns out that websites as well as the hidden so-called third parties that track us online can ask your browser for the entire list of fonts or extensions that you've ever installed. And that list could be different from almost anybody else on planet Earth. And so that might present a nearly unique or completely unique fingerprint of your device that can help a website or a third-party tracker recognize you when you come back. ...

These fingerprinting techniques are not directly getting at what sort of person you are; they're merely trying to develop some sort of recognizable pseudo identity of you. ... If you have this pseudo identity based on the fingerprint of your device, then what the website is going to be able to do is piece together all of the online breadcrumbs that you've left in different places and compile that into a profile, into a dossier of you. And using that, they can apply algorithms and infer your interests and preferences and so on.

On how fingerprinting can follow you across devices

This is best seen if you think about you as a traveler with two different devices, let's say your laptop and your mobile phone. What some website or tracker is going to observe is that there are two different devices over and over again connecting from the same networks, from the same set of IP addresses. ... Over time, that allows this online tracker to put together a profile of the behavior of those two devices and infer statistically, with a very high degree of confidence, that this pattern of coincidences could not have happened by chance — it must be because these two devices belong to the same individuals. ...

For the most part, these are very new and interesting technologies, but also creepy from a privacy perspective and more-or-less unregulated.

On the uses of online tracking

The most obvious consequences are certainly going to be online ads that you see and targeted offers that you get. Occasionally, we know that websites have been experimenting with price discrimination based on your online activities and trying to infer if you're a more affluent or less affluent type of consumer online. That's not so widespread yet, but there are a few studies that have revealed that it does happen from time to time. ...

Increasingly, people are discovering new uses for all of this online tracking information. For example, there are concerns that political campaigns might be using this data to specifically, individually target political messages to us. To the point where someone else might be getting a slightly different message that is tuned to their tastes or political proclivities or whatever. This has implications for democracy, and we need to have the societal conversation about this.

On ways to combat tracking technologies

There are many extensions that you can install in your browser that are going to block all of these online tracking technologies. One of them is Ghostery that we studied in our paper. There are a variety of others. The Electronic Frontier Foundation has released one called Privacy Badger. And these are tools — some of which I use myself and my colleagues employ — that are going to cut down on tracking. Although they come with some trade-offs. Occasionally one of the websites you're visiting might break, might not work exactly as you wanted it to. ...

These measures are a sort of Band-Aids. We do need systemic solutions, but that conversation is not happening yet.

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