This snitch is lurking inside the vast majority of colour laser printers even though most users have no idea it is there. The reason nobody is meant to know is that governments and other bodies use the information provided by colour laser printers to help identify who has copied or leaked information. The recent arrest of an NSA contractor named "Reality Winner" was down to her not realising, or perhaps not caring, that the documents she copied contained a hidden code that helped to reveal where and when the document had been printed.

You may be wondering how this is possible so let me explain. For at least 20 years, but probably longer, colour printers have been printing a hidden code onto every page they print. The majority of colour laser printer manufacturers have built this feature into their colour laser printers because failure to do so means no sales to many governments. All the major brands now incorporate this feature so the chances are that it will be hidden in any colour laser printer you use.

It's a very simple yet clever system and it has proven to be extremely effective in a number of cases. The printer will print a block of very small yellow dots that make up a binary pattern. A small block of yellow dots on a white background are all but impossible to see due to their limited contrast and that is why the majority of users remain unaware of them. It's often called Forensic Watermarking and there are other methods to do this but the yellow dot method is the one most commonly found on colour laser printers.

The coded pattern of dots includes the printer serial number and the date and time the page was printed. It also includes parity information to assist with the recovery of the data if some of the dots are corrupted or missing. This hidden watermark will be on every printed page making it much easier to trace the exact printer used and the date and time the job was printed.

One way to make the dots more visible is to look at a page under pure blue light. This works because the blue light makes the dots appear black. Using this technique a person with good vision should be able to see the dots. If you want to see an example of the dots and how they have been recovered then go to:

http://blog.erratasec.com/2017/06/how-intercept-outed-reality-winner.html

This article uses the same document that Reality Winner printed out and ultimately led to her arreste. The author uses an Apple computer but you should be able to follow the instructions with almost any system.

The Electronic Frontier Foundation has a rather outdated list of printers it has tested to see if they produce the yellow dot watermarks. Take a look and you will see many of the well known manufacturers in the list. You can find it here:

https://www.eff.org/pages/list-printers-which-do-or-do-not-display-tracking-dots

If you have a colour laser printer and your manufacturer is in the list then the chances are very high that your laser is producing a forensic watermark. In principle I have no problem with the forensic watermark feature itself and I can see that in certain situations it can be very useful.

However, I have a big problem with any feature that produces information, hidden or not, without the knowledge or permission of the owner to do so. This is the sort of thing that you imagine being done in a totalitarianism state and would probably have Eric Arthur Blair spinning in his grave. If you don't know who Eric Blair is just think of 1984.

If you need to print any document without it being traceable back to a specific printer then don't print it on a colour laser printer. Use a monochrome printer as these cannot produce the yellow dot patterns. Of course even these may be able to produce a forensic watermark but if they do then nobody seems to know about it. Or do they...