Please see the links below for details on a remote firmware update vulnerability that affects HP laserjet printers. Instructions are available to mitigate the exposure.
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c03102449
VULNERABILITY SUMMARY
A potential security vulnerability has been identified with certain HP printers and HP digital senders. The vulnerability could be exploited remotely to install unauthorized printer firmware.
The link provided above provides limited information. More extensive information is available from the following URL on securing HP printers
http://h71028.www7.hp.com/enterprise/downloads/HP-Imaging10.pdf