[EFF WWW spytech] Secret Code in Color Printers Lets Government Track You

From EFF.org:

A research team led by the Electronic Frontier Foundation (EFF) recently broke the code behind tiny tracking dots that some color laser printers secretly hide in every document.

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.

"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 yourself you'll need a blue light, a magnifying glass or a microscope (for instructions on how to see the dots, see: http://www.eff.org/Privacy/printers/docucolor/).