TechTok #6. How to deal with fingerprinting

We continue our TechTok series where we answer your questions about technology. In the previous editions we touched upon VPNs, DNS, ad blocking (of course) — today it’s time to talk about tracking, and more specifically, fingerprinting. The first question by an anonymous user will help kick things off:

Could AdGuard offer a service that masks my mobile fingerprint to make it as common as possible, preventing algorithms from manipulating prices or availability based on my device or behavior?

Let’s start by defining what a mobile fingerprint is. In real life, a fingerprint is a unique image of your fingertip, used for identification (think biometric passports). Online, a fingerprint is a more or less unique combination of your device’s characteristics, including its hardware, the software installed on it, and your settings. Such a combination can be used to track, profile, or personalize your online experience. Now, after we’ve got the basics out of the way, let’s see what your mobile fingerprint is exactly made of.

First of all, it includes device information, such as details about your phone’s make and model, OS version, device type (for example, whether it’s a smartphone or tablet), screen size, and resolution. These are hardware details that remain relatively constant. However, more information is gained from your device’s software and network characteristics. This includes your IP address, Wi-Fi network name, mobile carrier, and app data (such as the apps you have installed, their versions, and your usage patterns). The browser you use, its version, as well as the plugins and extensions installed — all of this also counts. A special mention deserves built-in sensor data and behavioral data (even how fast you type). This is already a large number of parameters, and we haven’t even covered them all! As you can see, some of these characteristics are way more consistent than others, and when we talk about fingerprinting we first and foremost mean the combination of hardware and software because it does not change a lot. While things like IP address and your Wi-Fi network name can contribute to the fingerprint, they are not as unique or reliable.

So, in short, each detail that deviates from default device settings makes your fingerprint more distinct, and consequently, easier to track. Now, back to your question as to how to make it more common and whether AdGuard can help you with that.

AdGuard products, including the ad-blocking apps, VPN apps, and extensions, weren’t specifically designed to protect users from fingerprinting. However, they can help you to make your fingerprint less distinct, which can reduce tracking, and, therefore, the ability of vendors to manipulate prices or availability of certain services. For example, AdGuard VPN can mask your IP address, preventing websites and apps from knowing your real location or IP-based details.

Additionally, you can enable several settings in the AdGuard Ad Blocker app that will help you hide in the crowd. The app lets you hide your user-agent string, replacing it with a generic version, which removes identifying details about your device like its model, OS, and browser version. And if you’re not using a VPN app, you can still mask your IP address by enabling mask your IP address setting in the AdGuard ad-blocking app. Additionally, you can also remove the X-Client-Data header, a piece of data often used by Google to track user activity.

A general recommendation would be to be selective with the apps and add-ons you install. The more you have, especially the less popular ones, the more unique your mobile fingerprint becomes. Since it’s not just about your fingerprint not standing out — but also about it getting tracked by third-party scripts — privacy-focused browsers like Brave and apps like AdGuard and Blockada may come in handy. They will block fingerprinting scrips from loading in the first place. However, be aware that every new extension you add or app you install risks making your fingerprint more unique.

A question from Sanjay Nayak will help us follow up on how to fight against fingerprinting:

How do you manage browser fingerprinting so that you do not stand out from the crowd? Is there some config that we can set in AdGuard that will ensure that all users will have the same fingerprint for their browsers?

This question is a little tricky, as the answer to it depends on what exactly you mean by “browser fingerprinting.” When a website wants to build your digital fingerprint, all it can interact with is your browser, so any fingerprinting it does will technically be “browser fingerprinting.” And we’ve already shared some general tips on how to use AdGuard to make your fingerprint less distinct, so maybe it would be better to elaborate more on some of the AdGuard settings aimed directly at manipulating your fingerprint.

The first one is called “Hide User-Agent,” and it can be found in AdGuard apps for all platforms except for iOS, where there are a lot of restrictions in place set by the operating system itself. Note that AdGuard browser extensions don’t have this setting too, since extensions’ functionality is being limited by the browser. User-Agent HTTP header, which is its full name, is a string that helps websites identify the operating system, the browser, and the platform the browser uses. A typical user-agent string can look something like this:

Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0

Let’s decrypt this string:

• Mozilla/5.0 is a general token used for historical reasons
• Windows NT 6.1; Win64; x64; rv:47.0 gives information about your operating system
• Gecko/20100101 denotes the browser engine
• Firefox/47.0 indicates the version of your browser

AdGuard allows you to enter any string to be presented as your user-agent. You can even remove some parts altogether (leaving the string empty will do exactly that). However, as most users don’t manually alter their user-agent, having an empty string for it might have the opposite effect — it will make you stand out more. So what are some good user-agents to use? Naturally, you want to present yourself to be as generic as possible. There are websites like this one that offer a selection of common user-agents to choose from. Be aware of choosing a user-agent that’s too unique, as it won’t do you any favors and you’ll end up worse than if you wouldn’t have changed anything at all. Another sneaky thing you can do is to switch your user-agent regularly to make it harder for websites to profile you. It is more time-consuming but may be a good option for more privacy-oriented users.

Another way to directly mitigate the harm fingerprinting inflicts to your privacy is to enable Tracking Protection filter in the Ad Blocking section of AdGuard settings. Your fingerprint may be the most unique of all, but if websites never get hold of it, it’s not going to help them track you. The Tracking Protection filter contains rules aimed specifically at preventing fingerprint-collecting scripts from doing their job. It’s not foolproof, as there are a lot of such scripts and you can’t cover them all, but there is really no reason not to take advantage of this weapon in your arsenal. Sadly, the limitations of iOS throw a wrench in the works again: Apple doesn’t allow ad blockers to execute complex rules required to block these scripts on iOS.

To wrap things up with this question, there is no magic button that would make every AdGuard user look like agent Smith from the Matrix. But follow the advice we gave you and you’ll make those who seek your digital fingerprint really work for their meal.

A user with an awesome name grumpy alpaca will help wrap things up with this question:

Is AdGuard participating to make my mobile fingerprint even more precise by exposing things like my use of AdGuard browser extension? My use of AdGuard app? What about AdGuard DNS?

As mentioned earlier, the more apps and extensions you have installed, the more unique your fingerprint becomes. There are also fingerprinting techniques that specifically target extensions. The same applies to switching to a less popular DNS server from your default one. Ultimately, it all comes down to how many users share the same combination of hardware and software with you. Since AdGuard products have millions of users, the chances of being identified solely because of their use are minimal.

It’s an unavoidable trade-off between utility, functionality, and how distinct your fingerprint is. Using an AdGuard extension, app, or the ad-filtering DNS server blocks most known fingerprinting libraries from accessing your device’s fingerprint, reducing tracking. This works for every system and platform apart from iOS. To block fingerprinting scripts from loading, you need to make sure that you have the Tracking Protection filter enabled.

At the same time, the simple act of installing the extension or the app makes your fingerprint less common. It’s a balancing act, and ultimately, it’s up to you to decide whether the features that protect from tracking mitigate the effect of your fingerprint becoming more distinct.

We’ll come back with more answers in the next issue of TechTok — send us your questions about any technology-related topic over through this form, and you might see them featured in the next TechTok!