Online Trackers Follow Our Digital Shadow By 'Fingerprinting' Browsers, Devices : All Tech Considered Online tracking is no longer about "cookies." New technology helps trackers link online breadcrumbs — including across devices — through browser settings, battery levels and other details.

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

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As we surf from website to website, we are being tracked. That's not news. What is news - and we learn it from researchers at Princeton University - is that the tracking is no longer just about cookies that aim to record our tastes. The researchers surveyed a million websites and found that state-of-the-art tracking is a lot more sophisticated than cookies.

They write about websites tracking the fingerprints that our devices leave. Joining us now is Princeton's Arvind Narayanan. Welcome to the program.

ARVIND NARAYANAN: It's great to be here.

SIEGEL: And what are my fingerprints or the fingerprints that my devices leave?

NARAYANAN: These things can be hard to visualize. But let's say you have a new computer that as far as you know is identical to the computer of the person sitting next to you. But over time you browse different websites, and you might install different fonts and extensions on your web browser.

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 presents a fingerprint off your device that can help a website or a third-party tracker recognize you when you come back.

SIEGEL: To what end? They can - I understand if I'm hacking into someplace where I'm unwelcome, it would be useful for them to recognize me. But what else would they do with all of that information, the fonts that I've added and the like?

NARAYANAN: Primarily this is being driven by online advertising technology. Being able to recognize you as you browse from site to site allows these online ad tech companies to build up a profile of your interests and things that you've done in the past and so on.

So if you've ever encountered, for example, adding a pair of shoes to your shopping cart and then you find that an ad for those shoes follows you around the web, all of that is driven by these types of fingerprinting and other online tracking technologies.

SIEGEL: If fingerprinting is that effective, that should mean that when I am working on my personal laptop computer at home and when I'm working on the laptop that I work on here at the office, something about what I'm doing would make it evident to some third party that I'm the same person.

NARAYANAN: That can indeed happen sometimes. So 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. And so 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.

And so 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.

SIEGEL: Is there something that I can do when I go online that would make me harder to track any countermeasures that I as a consumer or a reader can take?

NARAYANAN: Certainly 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 imply that are going to cut down on tracking. Although they come when some tradeoffs. Occasionally one of the websites that you're visiting might break, might not work exactly as you wanted it to.

SIEGEL: Arvind Narayanan, thank you very much for talking with us today. This was great. Thank you very much.

NARAYANAN: Arvind Narayanan is an assistant professor at Princeton's department of computer science.

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