ZXX is a computer 'font'--a group of typefaces for digital use--created by artist Sang Mun that currently result in illegible printed material when scanned by OCR technology that existed when it was initially produced. This qualification--when it was produced--is actually very significant to this kind of project because the various letter forms are (as with any typeface) 'set' and so will remain constants even though their size, arrangement and contents will inevitably vary from use to use: because these letter forms are a finite value, and are generally known, it would be relatively easy for a high powered OCR system to have this 'font' simply become one of the things it scans for, then error corrects so the contents become machine readable.
As and art project, it is amusing and timely, but it also fails to understand the issue it "solves." There is perhaps a better way to produce the same effect:
Instead of a set 'font' why not instead produce a plug-in that would randomly combine and remix both the letter forms of several fonts with noise, while at the same time embedding the actual content into those OCR in-compatible designs? The result would almost certainly be more secure than ZXX. Instead of being functional, this proposal seems more like wishful thinking than a real form of security; a variation of security through obscurity.