Techopedia explains
High-Energy Radio Frequency Weapon (HERF)
A HERF blast is a highly concentrated blast of electromagnetic radiation that can completely erase a hard disk, crash the PC or even fuse the silicon barriers on the chips, rendering the computer useless. However, in most cases, a HERF gun does not damage a computer permanently.
Most electrical appliances are at risk of this type of attack, although most electronic equipment in airplanes and other military vehicles is resistant to it.