This Recommendation presents guidance on: ?establishing the threat level presented by an intentional High Power Electromagnetic (HPEM) attack on an electronic equipment or system; ?the physical security measures that may be employed to reduce this threat level; ?establishing the vulnerability of the equipment (or system) to be protected from an HPEM attack. When establishing detailed countermeasures to HPEM attack@ it is extremely important that the threat level (strength) of the attack be adequately estimated: under-estimation means that the applied countermeasures will be insufficient and hence increases the risk that equipment may malfunction; whereas over-estimation means that the applied countermeasures may add significant (and unnecessary) cost to the equipment or system. Estimation of the threat level (strength) is calculated using sources such as the IEC standards as well as independent market studies performed during the preparation of this Recommendation. The vulnerability of the equipment (or system) to be protected is based on either: an assessment of the standards that the equipment (or system) satisfy or the results of independent evaluation (i.e. test) for a sample device. The threat and vulnerability levels considered within this Recommendation reflect the technology levels current as of March 2004. Hence it is expected that this Recommendation will require periodic review in the light of ongoing technological change to remain current.