Imagine that every time you print a document, the printer automatically includes a secret code that could be used to identify the device — and, potentially, the person who used it. Sounds like something from a spy movie, right?
Unfortunately, the scenario isn’t fictional. Most color laser printers and color copiers are designed to print invisible tracking codes across every single printed page of their output. These codes reveal which machine produced a document and, in some cases, when the document was printed or copied.
A Machine Identification Code (MIC), also known as printer steganography, yellow dots, tracking dots or secret dots, is a digital watermark that certain color laser printers and copiers leave on every printed page, allowing identification of the device which was used to print a document and giving clues about the originator.
Developed by Xerox and Canon in the mid-1980s, the existence of this technology became public only in 2004.
In 2018, scientists developed privacy software to anonymize prints in order to support whistleblowers publishing their work, but not before one whistleblower was caught sharing a top-secret National Security Agency report exposing previously undisclosed details about a months-long Russian hacking effort against the U.S. election infrastructure.
When Reality Leigh Winner sent classified documents detailing Russian hacking efforts during the U.S. election to The Intercept in 2017, she probably never imagined that the printer she used would give her away. But that’s exactly how the FBI says it was able to find and arrest her less than a month later.
Winner, 25, was an independent NSA contractor working for the national security firm Pluribus International Corp. with top-secret security clearance at an unnamed U.S. government facility in Georgia.
The FBI issued a warrant for Winner’s arrest three days before The Intercept published its article based on the documents.
Unbeknownst to most people, many new color laser printers secretly print all-but-invisible yellow dots on documents, which can then be decoded to identify when and where the documents were printed. This was the case with the memo that Winner printed.
The U.S. government has been able to convince a number of printer manufacturers to include these watermarks on all color documents, in a purported effort to prevent counterfeiting.