Abstract： Industrial control systems are ubiquitous and integral to social infrastructures such as our electric and water utilities， and our oil/gas， chemical， pipeline， and transportation systems. Not surprisingly given the violence and destruction reported somewhere in the world every day， the security of these distributed control systems （DCS） or supervisory control and data acquisition （SCADA） systems has become increasingly critical. An attack on these DCS would be potentially more disastrous than an attack on computer systems simply because DCS and physical plants have a direct and immediate impact on our well-being and day-to-day lives. Most recent security measures have only aimed at protecting the confidentiality， integrity， and availability of a system and its related networks. A critical area has been overlooked for too long： the sensor card or field IO module.

　　Since the discovery of the Stuxnet worm just a few years ago，1 we have become more concerned and more vigilant about the security of our critical infrastructures and the DCS systems which control them. While there are a lot of moving parts to the Stuxnet story， it is known that the worm spreads via a USB thumb drive.2Consequentially， architects of industrial systems must now take deeper security measures to protect their systems. All good.。.however， most recent security measures have only aimed at protecting the confidentiality， integrity， and availability of a system and its related networks. A critical area has been overlooked for too long： the sensor card or field IO module.