updated 10/17/2005 6:36:45 PM ET 2005-10-17T22:36:45

Just because a document from a color laser printer doesn't carry your name doesn't mean no one can trace it back to you, privacy advocates warn.

The Electronic Frontier Foundation says it has cracked the tracking codes embedded in Xerox Corp.'s DocuColor color laser printers. Such codes are just one way that manufacturers employ technology to help governments fight currency counterfeiting.

"Underground democracy movements ... will always need the anonymity of simple paper documents, but this technology makes it easier for governments to find dissenters," said Lee Tien, EFF senior staff attorney. "Even worse, it shows how the government and private industry make backroom deals to weaken our privacy by compromising everyday equipment like printers."

Researchers found patterns of yellow dots arranged in 15 by 8 grids and printed repeatedly over every color page, said Seth Schoen, a staff technologist at the San Francisco-based civil-liberties group.

The dots are visible only with a magnifying glass or under blue light, which causes the yellow dots to appear black.

By analyzing test pages printed out by supporters worldwide and by staffers at various FedEx Kinko's locations, researchers found that some of the dots correspond to the printers' serial numbers. Other dots refer to the date and time of the printing.

Xerox spokesman Bill McKee would not provide details about the technology. He said the company "does not routinely share any information about its customers," though it does respond to requests from law enforcement.

At the Secret Service, which helps develop such technologies with other government agencies and industry, spokesman Eric Zahren said the tools are designed "simply to make it more difficult to utilize that equipment for the illegal activity of reproducing genuine U.S. currency."

"They do not in any way track the use of a personal computer or a person's computer's hardware or software," he added, refusing to elaborate on the technologies.

But Schoen said much can be gleaned from the printouts alone.

Consider two documents, one carrying the author's name and one meant to be anonymous. By comparing the codes, it can be determined whether the two documents came from the same printer, even if Xerox reveals nothing about a customer's serial number, Schoen said.

The EFF is now studying other printers from well-known manufacturers with similar tracking codes, but whose keys remain secret.

The Xerox DocuColor printers are high-end machines more likely to be found in offices and copy centers than in homes.

The U.S. government is involved with other countries in a separate anti-counterfeiting program meant to prevent currency from being scanned and printed.

Adobe Systems Inc. has acknowledged quietly adding the government software to its Photoshop software at the request of regulators and international bankers.

But David Skidmore, a spokesman at the Federal Reserve Board, said that the technology, known as the Counterfeit Deterrence System, was aimed mostly at personal computers and ink-jet printers — not the high-end machines like DocuColor.

Copyright 2005 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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