Could Your Printer Be A Security Risk Because It Saves A Copy Of Your Data?

All printers built in the last 20 years (at least) have built-in memory, but only in the last decade have home and small office printers started to store your documents in semi-permanent memory. Most of the time that isn’t a problem—nobody wants to steal the funny cat picture you just printed—but it can be a security risk when you print confidential documents.

Why Printers Store Your Data

Here’s a fun trick: print a multipage document to your USB or Wireless printer. After it starts printing, gently pull out the USB cord or disconnect your computer from the wireless network. In most cases, the document will keep printing, indicating your printer is printing it from its memory instead of from the computer directly. This is a feature common to almost all modern printers.

Printer manufactures didn’t design this feature because they wanted to serve people who trip over their cords or have bad wifi; they added memory to printers for three reasons:

1. To make printers print a little faster. Memory lets a printer accept the document from the computer as fast as its connection allows, so even if the computer slows down later (maybe because you decided to play a game), the printing won’t slow down.
2. Most modern color printers work by combining together different colors of ink in a marvelously complicated process. To make this work as well as possible, each printer has a sophisticated printing language which describes how the document should look. Modern printing languages are almost all almost programming languages so the computer can exert full control over how the printer works, but to run a computer program, the printer needs to load the entire program into its memory before it can start running (and printing) any of it.
3. In addition, many modern printers support more than one printing language. For example, high-quality printers designed for business tend to support not just their own native language (usually called PCL, or Printer Command Language) but also Adobe Postscript (PS), which actually is a programming language widely used for even non-printing tasks, such as being the language Mac OSX uses to display 2-D windows.

Where Printers Store Your Data And What To Do About It

Similar to computers, printers have both volatile memory (like computer RAM) which gets lost when you turn the printer off and non-volatile memory (like computer hard drives) which sticks around until it’s deleted.

The volatile memory isn’t an issue unless you need to worry about the police suddenly raiding you house. To purge volatile memory, just unplug your printer for 60 seconds or more.

Non-volatile memory is what you need to worry about if you just printed a confidential document. Printers tend to use their memory as what programmers call a circular buffer: data gets written in each sequential part of the memory until it gets to the end and then it starts at the beginning again, seeming to go in a circle.

So if you just printed a scanned copy of all your credit cards and now you want to sell your printer on eBay, you need to print enough non-confidential documents to use up the whole circular buffer. On business printers with non-volatile memory measured in gigabytes, this can take a long time. On home printers, you can usually just print 5 to 10 complicated documents, such as pictures or anything else besides plain text.

Oh, and there’s a nifty trick which can save you lots of ink: keep your old ink cartridges. When you need to clear out your printer’s memory, take out your full ink cartridges, put in the old cartridges, tell the printer to stop complaining about low ink, and print as many pages with as much color in them as you need to clear the memory. Then put your full ink cartridges back in so you can print like normal. It’s kind of a pain, but it can save you $10 or more in ink costs each time you clear your printer memory.