Is your printer spying on you? 

Yes, it is. So is your mobile phone, your automobile, and your web browser.

Machines keep trackable records in their memory banks. Most of the time these records are never used. They are destroyed or wiped clean when electronic devices are trashed or recycled.

However, if you ever find yourself involved in an investigation, your devices provide clues about how they were used. We’ve seen countless examples of police tracking cell phones and credit cards to solve crimes. 

Your printer has a story to tell too.

Printer Forensics

A niche branch of forensic science, printer stenography examines the history of printers and copiers. Using digital clues, scientists determine which specific machine printed a certain document, and what time it was printed. 

After printer forensics outed Reality Winner as a government whistle blower in 2018, people started looking twice at their unassuming office printers…and whistleblower activists began scrambling for software encryption solutions.      

Printer stenography is not new. Your color laser printer has been tracking you for decades. The makers of color copiers introduced the Machine Identification Code in the mid-1980s in an effort to stop counterfeiters.

The Machine Identification Code

Imagine you work for Xerox in the mid-1980s. Business is good. Your new line of color laser printers has everyone excited…except for the United States Treasury. 

Your high-resolution color printers concern the United States government — as well as government treasuries around the world. They’re worried your printers could be used   to produce counterfeit money. They’re so concerned about it, in fact, that they won’t allow you to import your laser printers from Japan unless you develop an anti-counterfeiting protocol.

As a result Xerox developed the Machine Identification Code (MIC). The MIC is a unique printer number represented by a repeating series of yellow dots printed on every page that printer prints. The dots appear as tiny black spots when viewed under ultraviolet light but are invisible to the naked eye.

In addition, software embedded in color scanners recognizes the yellow dots on American cash, preventing bills from being scanned. Xerox was granted U.S. Patent No 5515451 for the MIC, which prevents counterfeiters from scanning real money or printing a convincing copy. 

The MIC Catches Criminals

In October 2004, PCWorld reported Dutch authorities caught two counterfeiters by tracing the hidden yellow dots back to their Canon laser printer.

Within months, civil rights group Electronic Frontier Foundation began decoding the MIC. Once deciphered, the grid of yellow dots revealed the date and time the document was printed. It also revealed the serial number of the machine it was printed on.

Manufacturers not only began acknowledging using the MIC in their products, they used it as a selling point. In 2011, Xerox color printers included this in its product description: 

“The digital color printing system is equipped with an anti-counterfeit identification and banknote recognition system according to the requirements of numerous governments. Each copy shall be marked with a label which, if necessary, allows identification of the printing system with which it was created. This code is not visible under normal conditions.”

The MIC Catches Whistleblowers

In August 2018, Reality Winner, a former intelligence officer, pled guilty to leaking classified documents to a news outlet. Investigators used the MIC on the documents to determine when and where they were printed. Crossed reference with security footage revealed Winner as the whistleblower. The report Winner leaked allegedly showed evidence of Russian interference in the 2016 United States presidential elections.

Evolution of the MIC

Machine identification codes evolved with the times. In 2018, scientists at the TU Dresden analyzed the patterns of 106 printer models and found four different coding schemes.

While privacy advocates seek ways around the MIC, government agencies and printer makers keep one step ahead. Changes in laser intensity and text shading can also be used in printer forensics. However it is unknown if such methods are being employed.

In addition, the EURion constellation (or Omron rings) is a pattern printed on banknotes worldwide. Color copiers recognize the pattern and prevent currency from being copied and counterfeited. 

Going Off Code

If you aren’t comfortable with a printer that uses MIC, buy an older model that does not use it. HP Color Laserjet 4500 and 8500 series of printers don’t display tracking dots. In addition, the Samsung CLP 500 series and several models of older Oki laser printers are MIC-free. Any new color laser printer bought today will likely display MIC dots. 

However, there are other ways to avoid the Machine Identification Code. Print and scan documents in black-and-white, or convert documents to black-and-white using an image editor. This eliminates trackable yellow dots. 

In addition, it appears that inkjet printers and monochrome laser printers do not use the MIC. It’s unknown if inkjets and monochrome laser printers use another type of forensic tracking.

The EFF raised civil rights questions about how the MIC could be used against law abiding citizens. 

“Individuals using printers to create political pamphlets, organize legal protest activities, or even discuss private medical conditions or sensitive personal topics can be identified by the government with no legal process, no judicial oversight, and no notice to the person spied upon.”