Updated 4 months ago by Yana Shch

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Fonts fingerprinting is a set of identification methods based on what fonts you have and how they are drawn inside your browser. Generally, there are two methods by which websites are able to identify fonts:

  1. Measuring font metrics
  2. Fonts list enumeration
Unique identification based on font metrics measurement is similar to the Canvas fingerprinting algorithm. The technique of using fonts is less efficient, since the Canvas receives not only the measurements inside the bounding boxes, but also the data about the drawn pixels (read more about Canvas here).

Fingerprints test

You can test how the first and second method work on the Browserleaks test website.

Fonts list enumeration

The most popular way to gather the list of fonts installed on your machine is through CSS introspection. In short, this method can derive the list of your fonts by measuring the width of a phrase produced by your browser in a specific font. If the width matches, it means that you have that font installed. If it doesn't, it can be determined that the font is missing.

By cycling through the list of possible fonts and widths, websites can get an accurate picture of which fonts are installed on one's machine.

How it works in Multilogin

Multilogin utilizes a special algorithm that combats such methods and allows you to control which fonts the websites can enumerate. When you create and save a profile, Multilogin will automatically generate a random list of fonts, which will be displayed on the end websites.

You also have the option to edit the list one by one by clicking on the “Edit” button.

Did you know that websites can also use Flash or Java Applet plugins to obtain your system fonts list, which is then silently transferred to a server in the background through AJAX? Well, they can! So, be always careful when enabling plugins in your browser profiles. You can find more information about this here.
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