Techworld has a DEFCON22 review of the 10 scariest hacks.
If a printer can be hacked on the network, all the things you scan or print can be stolen, and once the hacker is on the network there can be additional hacks to gain additional control of your machines.
Irongeek story on HPJetdirect hacks
By default HP OfficeJet devices are not password protected. There are many “help” pages on the Internet discussing how to hack a printer to fix a configuration issue, so what a bad hacker can do is to find out what type of printer it is and then find the hack to control it.
Every device needs to be locked down as much as possible, to thwart the hacker knocking on your door.
Contact Us if you do not know how to do this, as we can help