The simple answer is... you can't...
Browsers download font files by default by visiting your site as they need those files to be able to render your custom fonts. The font types eot, woff, opentype and svg does not use any DRM protection, and as far as I know, no other font does for that matter... because of this you can't protect your fonts.
You can however make it harder for them using, or make them more aware that your fonts are copyrighted, several methods include:
- HTTP referrer checking
- Obfuscation
- Data URIs
- Visible license data
- Segmenting and subsetting
At the end of the day, if someone wants to steal your fonts they will, accept that or don't use them on your website.
