High-power microwave (HPM) sources have been under investigation for several years as potential weapons for a variety of sabotage, terrorism, counter-security system, and combat applications. The key points to recognize are the insidious nature of HPM and the many areas in which it can impact on security technology. Computers and other equipment can be damaged without user recognition of the cause. HPM has the capability to penetrate not only radio front-ends but also the most minute shielding penetrations throughout the equipment. The potential exists for significant damage to security and other devices and circuits, and even injury to humans. Different HPM threats are described and specific protective measures are outlined. >