If you considered yourself a happy owner of a color laser printer, you probably won’t be so happy any longer.

In 2005 Electronic Frontier Foundation, an organization supporting customers’ freedoms in the world of electronics, made a discovery that didn’t have much publicity. Every document printed on most color laser printers includes a set of yellow dots used to identify the printer. These dots are invisible to naked eye, but can be clearly seen under microscope or intense blue light.

The dots make up a pattern unique to each printer, so it’s possible to identify the serial number, make and model of printer. Given that most of color laser printers sell directly from the manufacturer or through well-documented service providers, it becomes easy to track the owner of printer. So, everything you print can, and pretty much will, be used against you.

Why on earth, something like this would happen? One of the reasons why might be an agreement of US government and most printer manufacturers to help track down currency counterfeiters. Technological advancement of printing and photocopying devices made it easier to forge money, and with the yellow marks the counterfeit can be tracked back to its origin.

On the other hand, the same technique may be used to track any other printed materials, including those you considered personal. No law requires printer manufacturers to use that kind of embedded markings. No law prevents government services from tracking and collecting the information using these markings.

However, there is something you can do about this. Remember that color laser printers don’t make hidden dots, if printing in black-and-white mode. Monochrome laser printer, as well as inkjet and dot-matrix printers are also dots-free. The Electronic Frontier Foundation maintains and regularly updates a list of printers that do and don’t have the tracking dots. Just check it out to see if your printer is spying on you or not.