How tech sleuths cracked the mysterious code that turns your printer into a spying tool

You wouldn’t have noticed it unless you knew where — and how — to look, but the top-secret National Security Agency document leaked to the Intercept and published Monday contained a clue that may have led authorities to its source.

Spread throughout the pages were barely visible yellow dots, each less than a millimeter in diameter, repeated over and over in the same rectangular pattern. You could see them by zooming in on the pages and adjusting the color. Or, if you had the original printed papers, you could have inspected them with a magnifying glass and a blue LED light.

By Derek Hawkins

Full Story: https://www.washingtonpost.com/news/morning-mix/wp/2017/06/09/how-tech-sleuths-cracked-the-mysterious-code-that-turns-your-printer-into-a-spying-tool/?hpid=hp_hp-morning-mix_mm-printers%3Ahomepage%2Fstory&utm_term=.c3b55f15d0f0