This Recommendation presents guidance on: ? establishing the threat level presented by an intentional high-power electromagnetic (HPEM) attack on an electronic device 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 a HPEM attack. When establishing detailed countermeasures to HPEM attacks@ it is extremely important that the threat level (strength) of the attack be adequately estimated. Underestimation means that the applied countermeasures will be insufficient and hence increases the risk that equipment may malfunction; whereas overestimation 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 the independent market studies performed during the preparation of this Recommendation. The vulnerability of the electronic device (or system) to be protected is based on either an assessment of the standards that the electronic device (or system) satisfy@ or the results of independent evaluation (i.e.@ testing) of a sample device. The threat and vulnerability levels considered within this Recommendation reflect the technology levels current as of 2016. Hence@ it is expected that this Recommendation will require periodic review in the light of ongoing technological change in order to remain current.