Help Net Security The U.S. Secret Service admitted that the tracking information is part of a deal struck with selected color laser printer manufacturers, ostensibly to identify counterfeiters. However, the nature of the private information encoded in each document was not previously known. via EFF
'"We've found that the dots from at least one line of printers encode the
date and time your document was printed, as well as the serial number
of the printer," said EFF Staff Technologist Seth David Schoen.
'You can see the dots on color prints from machines made by Xerox, Canon, and other manufacturers.
The dots are yellow, less than one millimeter in diameter, and are
typically repeated over each page of a document. In order to see the
pattern, you need a blue light, a magnifying glass, or a microscope (instructions on how to see the dots).
'EFF and its partners began its project to break the printer code with
the Xerox DocuColor line. Researchers Schoen, EFF intern Robert Lee, and
volunteers Patrick Murphy and Joel Alwen compared dots from test pages
sent in by EFF supporters, noting similarities and differences in their
arrangement, and then found a simple way to read the pattern.
'"So far, we've only broken the code for Xerox DocuColor printers," said
Schoen. "But we believe that other models from other manufacturers
include the same personally identifiable information in their tracking
'You can decode your own Xerox DocuColor prints using EFF's automated program.'