There’s reportedly a new way for websites to spy on visitors: by monitoring how their computers’ SSDs behave. The technique is called FROST, short for “fingerprinting remotely using OPFS‑based SSD timing,” and it runs through JavaScript on a web page.
A malicious website can create a large file in the browser’s private storage. It can then repeatedly read from this file to check for small changes in the time it takes to access it. These timing changes occur because other programs and browser tabs are also using the SSD, creating competition for drive access, per Ars Technica.
By tracking these timing patterns and feeding them into a trained convolutional neural network, the attacker can determine which other websites and apps are open on the device. This works in different web browsers and can recognize common applications based on their input and output patterns. FROST does not read actual files or decrypt HTTPS traffic, but it can reveal what services run in the background.
So far, this looks more practical on paper (say, in lab conditions) than in real-world practice, where updates, background tasks, other software, and more can blur the pattern. There is also no public evidence that tracking or ad networks use this method today.
In the meantime, users who want to proactively protect their activity can reduce risk by limiting the number of untrusted tabs they keep open and separating sensitive browsing into dedicated profiles or containers.
