https://theoutline.com/post/1713/the-history-of-the-secret-printer-code-that-may-have-caught-the-nsa-leaker
JUN—13—2017 11:30AM EST
A once secret code, invisible to the naked eye, may have been one of the markers used to identify and eventually arrest NSA leaker Reality Winner. Security researchers have theorized that Winner’s downfall could have been a small set of dots in the corner of the Top Secret analysis she printed and mailed to online news outlet The Intercept.
Just by using a microscope on a document, Schoen could tell which Kinko’s in San Francisco it was printed from, but he wondered if he could determine the origin of any Kinko’s printed document in the country. EFF fans began heading out to their local Kinko’s and mailing Schoen their documents. Thanks to a volunteer who came into the EFF office to help analyze the patterns, they were able to realize the dots were just a binary code set in a grid. Not only that, but that these dots signified the printer’s serial number, as well as the date and time the document was printed. Then Schoen created a computer program which allowed anyone to punch in the dots they found on their documents to see what data they contain.
“There was kind of a disturbing moment back in 2005 when someone who read our website called the printer company and said ‘I want to know how to turn [microdots] off,’” Schoen says. That call resulted in a visit from the Secret Service.
Law enforcement agencies have worked to keep the method for identifying a printer based on its microdots secret, and now some printers use an updated version of microdots that are much more complex and spread across the page. That code has yet to be cracked.