A former NSA contractor has designed a typeface that would be unreadable by text-scanning software (either used by a government agency or an independent hacker).

Sang Mun’s response to the NSA surveillance leak was direct – he created four new fonts, called ZXX, aimed to disrupt the Optical Character Recognition (OCR) systems used by Google and others to analyze text, according to a CNN report.

The four fonts – Camo, False, Noise and Xed – were developed through a rigorous process of drawing and testing that kept the typeface illegible to computer vision but readable for humans by overlaying the characters with patterns such as dots or a neat X across each letter.

However, Ross Anderson, Professor in Security Engineering at the University of Cambridge Computer Laboratory, is skeptical of the fonts’ abilities to fool computer systems: “I don’t think any of this is more than privacy theater,” he said in the CNN article. “The fonts could probably be broken.”