A new online tracking tool may be shadowing you on the web

Science Friday
Mysterious keyboard

The seemingly endless arms race between Internet users and online data collectors has opened a new front: canvas fingerprinting.

Julia Angwin, the author of Dragnet Nation: A Quest for Privacy, Security, and Freedom in a World of Relentless Surveillance, recently published an expose on canvas fingerprinting for ProPublica.

She writes:

“[It] works by instructing the visitor’s Web browser to draw a hidden image. Because each computer draws the image slightly differently, the images can be used to assign each user’s device a number that uniquely identifies it.

Like other tracking tools, canvas fingerprints are used to build profiles of users based on the websites they visit — profiles that shape which ads, news articles or other types of content are displayed to them.

Canvas fingerprinting is used on websites from whitehouse.gov to youporn.com — and there is very little you can do to stop it, according to Angwin. There are “various types of software that you can add on to your browser that might block it,” she says, but typical measures consumers take to avoid tracking, like using the Do Not Track function of a website, clearing your cache and deleting cookies, will not prevent websites that use canvas fingerprinting from collecting the information they want.

Mobile phones are largely immune from canvas fingerprinting, Angwin notes, because their architecture differs from desktops, making them less easy to identify with canvas fingerprinting.

Another solution is a browser called TOR, which was initially developed with the US Navy. TOR lets people browse the internet anonymously, and has been used in nations like China to allow citizens to circumvent government-created firewalls. Recently, however, TOR announced that its security had been compromised.

Angwin says she was surprised by how pervasive canvas fingerprinting is, given that it was created only a year-and-a-half ago. Researchers at Princeton, whose study was the basis for Angwin's article, found it on five percent of the top 100,000 websites, she says.

Angwin was also surprised by the public response to her report. “[P]eople are really concerned about being followed around the web,” she says. “It is creepy when you're online and those ads follow you from place to place.”

Angwin was especially amused by the response of the online porn site, youporn.com. “After the article ran they said they were going to remove the company that was doing canvas fingerprinting from their website, because it was jeopardizing the privacy of their users,” Angwin says with a laugh. “I felt that I had done a great thing for porn users everywhere.”

Even if Internet users find an easy way to block canvas fingerprinting, this is by no means the end of the tracking “arms race,” Angwin cautions.

There are already commercial websites that will show you ads for items in specific price ranges based on information they have about other websites you have visited. Some even change the price of their goods based on your zip code. This is the new “cutting edge” of personal data use, Angwin says.

“This is what a lot of economists would say is the perfect pricing; this is the market economy at its very best,” Angwin notes ironically. “But I have this sneaking feeling that it's going to end up badly for me ... I just know somehow that I'm going to be the sucker who ends up having to pay more.”

But the ultimate tracking device that concerns Angwin is facial recognition.

“Forget about cookies,” she says. “Once you walk down the street and everybody can identify you...or you walk in the store and the store camera identifies you and they decide right away to pull up a whole database about your income and this and that — I feel that's going to change our social dynamic in ways I just can't imagine are going to be enjoyable.”

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