Cross-device tracking. De-anonymization of Tor, VPN, proxy users using audio beacons.

Cross-device tracking – a type of attack that allows tracking a user across multiple devices simultaneously. This has long been a dream for marketers, but this technology has also proven effective in de-anonymizing cybercriminals who use Tor, VPN and proxies to hide their real IP address.

In this chapter, I will discuss audio beacons – a very dangerous type of cross-device tracking attack that allows de-anonymizing VPN, Tor, or proxy users, even if they are doing everything correctly. You don’t need to delve into the depths of technical knowledge; you just need to understand the principle of how it works and the methods of protection.

You have probably encountered sociological surveys when someone calls your home and asks if anyone is currently watching television and, if so, which channel. In this way, for example, 1000 people are called, and the percentage ratio is calculated. This is needed by channels to, firstly, understand the interests of the audience, and secondly, to gauge reach – this is important for selling advertising.

This is also important for marketers to more accurately choose the timing of ad orders and assess the volume of views of the ordered ads. However, this method of data collection is expensive, has a high margin of error, and relatively low reach.

Now imagine that your voice assistant on your phone, which, as you may have noticed, understands live speech perfectly, will listen to the perimeter and determine which channel you are currently watching. For this, the advertisement on the channel will contain beacon phrases (for example, it will say "advertisement on the First Federal"), which the phone picks up and then sends information to the server that you are currently watching a specific channel or listening to a certain radio station.

This is a cheap and effective technology, but engineers want to make it even more sophisticated and use audio signals that the human auditory system cannot recognize. Judging by the presentations, engineers have made good progress in this. But we are not here for a marketing course, and this technology interests us solely as a tool for de-anonymization.

The site opened – and the hacker was caught

Imagine yourself as a very dangerous hacker being hunted by the FBI. You enter a trap site specially prepared for your capture. This is an absolutely harmless site; it will not carry out any attacks, it could even be a page of a popular site whose owner has created it in collaboration with the FBI just for you.