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Yellow Dots of Mystery: Is Your Printer Spying on You?

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Step 2: Blue light (w/ unaided eye) method

Picture of Blue light (w/ unaided eye) method

You'll need a blue light for this method. EFF has blue LED lights available, or you can get a blue LED flashlight or any other strong blue light from any other source. An ordinary battery-powered blue LED will work.

Turn off all the lights, and eliminate as much ambient light as possible. Shine a blue LED light on the blank part of the printed page. As examining a printer page under blue light improves the contrast, the yellow dots should appear black.

If you have good close-range vision, you should then be able to see them easily. They might initially look like small flecks of dirt or dust. If you can't see the dots this way, check to be sure that your printer is known to produce them, and try asking a friend to have a look.
 
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