How your ad blocker can follow you around the web

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Ah, ad blockers. Even if you are not one of the increasing number people downloading any of these plugins, chances are you’ve heard people singing their praises for all kinds of reasons. They make the web less crowded, less slow, less intrusive place to be. So naturally the money-hungry tech newbies have found a way to ruin these tools for their own profit.

Cybersecurity researcher Sergey Mostsevenko explained exactly how this type of system works in a blog post last month. As he said, the average ad blocker leaves tiny traces of data on the websites you visit. When these traces are collected en masse, a bad actor (or a tech company) could use these signals to identify your specific browser – a process literally called “fingerprints” in the targeting ad industry. And like a fingerprint, these signals are basically impossible to burn off without taking a few quite drastic not.

“Fingerprints” refers to a particularly shabby form of tracking designed to be almost impossible for users to shake. Cookies can be erased, your cache can be cleared and you can browse exclusively in incognito mode, but your browser’s “fingerprint” is cobbled together from a kill different signals: your IP address, your window size, your language settings and much more. When you visit a web page that has a hidden fingerprint code, those data points are sucked up and a jumble of hashed numbers and letters (your unique fingerprint) is spat out. By tracking which fingerprints appear on which sites, these companies can secretly follow you no matter how badly you beg them to stop.

Naturally, when you use an ad blocker, it will emit some sort of signal to the site you are visiting, but not enough to uniquely identify your browser. To do this, Mostsevenko explained, you have to get a little creative.

Ad blockers come in all shapes and sizes, but they all work the same – they look for specific things on a page (like a piece of ad code) and prevent them from showing. In order to find out what is worth blocking, most of the major ad blockers rely on different filter lists suitable for all kinds of ad nuisances you want to remove: German announcements, mobile ads, pop-up, and more. Some blockers even allow users to download their own filter lists if the available options are not sufficient. Much like different bouncers at different nightclubs, each of these listings will void their own collection of HTML snippets and ad URLs every time they are turned on.

There could be nearly 1 billion internet users blocking ads across the planet, but each of them uses an amalgamation of different tools and filters that’s probably different from the ad blocker sitting next to them. In short, it’s the first fingerprint fodder, with a bit of legwork.

Mostsevenko’s very long and very technical blog explains this work in depth, but the short version is: First, prepare the list of ad blockers you want to detect in website visitors and determine which elements each of them. these blockers blocks. Then add a small piece of code to a web page, like a strip of HTML code, that loads all of these different elements one at a time, somewhere out of view, keeping an eye on which elements load on the page and those who don’t. If the company that creates these fingerprint tools is tech-savvy enough, this job shouldn’t take more than a second.

Mostsevenko tested an example blocker detection program using Safari’s browser on a 2015 MacBook Pro to see how much delay it added to a web page’s load time. It took approximately 3 milliseconds to verify each item on 45 unique ad blocklists. Increasing that number to 400 lists took the program a whopping … 20 milliseconds to complete – a lag you probably won’t notice unless you’re genuinely interested. competitive console games.

“The list of filters that a person uses is only likely to change if they change their ad blocker or if their installed ad blocker gets a major update,” wrote Mostsevenko. But it will inevitably happen eventually. Filter lists get modified and modified by developers all the time. Ad blockers are reviewed once they are compromise or caught shooting their own patterns with personal data. These people may have a new computer, try a new browser, or reduce their text by two sizes. People can change, which means fingerprints based on ad blockers or anything else in our digital lives will never be perfect. But in a world where cookies are crumbling and app trackers are suffocation, data is data, and the data industry is always worth at least $ 200 billion. Your ad blocking data is of value to someone, somewhere, a fact that could give a weirdly dystopian self-esteem boost if you’re as brain poisoned as I am.

Capitalist hell aside, there are a few more steps you can take to prevent your browser, ad-blocked or not, from being taken by fingerprints. The Electronic Frontier Foundation suggest disable javascript as soon as you can and use a popular browser like Safari or Firefox which have each taken their clean not to cancel fingerprint attempts. Limit extensions to a minimum, invest in a good VPN, and no matter how much a website begs, always always refuse their cookies.


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