More manufacturers are outfitting laser printers with technology that leaves microscopic yellow dots on each printed page to identify the printer’s serial number – and ultimately, you, says the San Francisco-based Electronic Frontier Foundation, one of the leading watchdogs of electronic privacy.

The dots, invisible to the naked eye, can be seen using a blue LED light and are used by authorities such as the Secret Service to investigate counterfeit bills made with laser printers, says Lorelei Pagano, director of the Central Bank Counterfeit Deterrence Group.