Since late 2004, EFF has been warning the public about "printer dots" -- tiny yellow dots that appear on documents produced by many color laser printers and copiers. These yellow dots form a coded pattern on every page the printer produces and can be used to identify specific details about a document; for example, the brand, model, and serial number of the device that printed it and when it was printed. In short, the printer dots are a surveillance tool that can link each printed page to the printer that printed it.