Q. Is it true that laser printers put an invisible code that contains the printer’s serial number on every document printed?
A. Some, but not all, laser printers do leave a series of nearly imperceptible yellow dots on the printed page. These dots usually contain the encoded serial number of the printer and may also include the time and date that the document was printed.
The existence of these dots has long had privacy advocates worried. The Electronic Frontier Foundation, a privacy rights group, has been closely following the yellow dots issue because there are no legal provisions to stop government agencies from using the technology to track documents in cases unrelated to counterfeiting.