EFF probes printer watermarks

Color laser printers print hidden data that lets law enforcement agencies tell which printer was used and when, according to the Electronic Frontier Foundation. The EFF on Thursday sent a freedom of information act request to the U.S. Secret Service in an attempt to get details on the tracing feature, which the group says impacts the privacy of users.

"This undermines people's ability to speak and publsih anonymously," Seth Schoen, a staff technologist at EFF said Friday at the 13th annual Defcon hacker event in Las Vegas.

In the traditional EFF presentation at DefCon, Schoen placed a sheet of paper printed on a Xerox DocuColor printer under a microscope with a blue light. Yellow dots appeared. These identify the printer and when the print was made, Schoen said.

"If you actually print out a white page you would get a whole page with yellow tracking dots that you can't see with the naked eye," Schoen said.

The marking technology in printers was developed at the request of governments to deter counterfeiting activities using the machines, PC World reported in December. The Dutch government, for example, has used it to track counterfeiters of railway tickets, WebWereld, a Dutch technology news site, reported in late 2004.

Schoen isn't hopeful that the Secret Service will share details on the laser printer watermarks. EFF's lawyers probably have to go to court, he said.