"Modern weapons systems have depended on microelectronics since the inception of integrated circuits over fifty years ago. Today, most electronics contain programmable components of ever increasing complexity. At the same time, the Department of Defense (DoD) has become a far less influential buyer in a vast, globalized supplier base. Consequently, assuring that defense electronics are free from vulnerabilities is a daunting task. Because system configurations typically remain unchanged for very long periods of time, compromising microelectronics can create persistent vulnerabilities. Exploitation of vulnerabilities in microelectronics and embedded software can cause mission failure in modern weapons systems. Such exploitations are especially pernicious because they can be difficult to distinguish from electrical or mechanical failures and because effects can run the gamut from system degradation to system failure to system subversion. Cyber supply chain vulnerabilities may be inserted or discovered throughout the lifecycle of a system. Of particular concern are the weapons the nation depends upon today; almost all were developed, acquired, and fielded without formal protection plans."
Defense Science Board: http://www.acq.osd.mil/dsb/