Researchers at MIT are seeing red over the use of invisible yellow dots that printers embed in documents to help authorities track them to their source.

Most color printers today place invisible yellow dots on documents. The patterns help law enforcement groups figure out who printed a document. The practice has been used to bust counterfeiters, identify authors of ransom notes, and nab murderers.

MIT's Computing Culture Club has launched Seeing Yellow, a Web site dedicated to ending the practice, after discovering that someone had called their printer manufacturer for instructions on how to stop a printer from embedding the yellow dots and received a visit from Secret Service agents a few days later. The agents asked why the man did not want to be tracked, the group said in a statement posted on their Web site last week.

"Computing Culture wants to preserve the right to anonymous communication by fighting both printing dots and the government bullying used to sustain them," the group explained. "Our privacy and our control over our own technology is far too important to give up over trumped up fears of photocopied money."

The site states that the ability to speak anonymously is essential to a democracy. It gives details on printers that embed the dots (laser color printers), tips on how to spot them (using a bright blue LED and examining closely, possibly with a microscope), and urges people to contact their printer manufacturer with a series of questions and requests. It states that no law requires the companies to engage in the practice and recommends that people ask why the function is there and whether there are other covert tracking mechanisms.

"Ask them to stop using tracking codes and demand that they tell you how to turn it off," the group states. "The Secret Service can't come and question all of us!"

The site contains links to the Electronic Frontier Foundation's list of printers that create patterns the group has spotted.

Seeing Yellow reports that more than 1,000 people have called their printer manufacturers to complain.