Such bombs were reportedly used in the Gulf War. HERF stands for high energy radio frequency. In essence, HERF guns are nothing but special-purpose radio transmitters. HERF guns are able to shoot a high-power radio signal at an electronic target and put it out of function. The damage can be moderate or severe, depending on the amount of power used.
Moderate damage is when a system shuts down but can be restarted.
Severe damage is when the system hardware has been physically damaged and must be replaced. Electronic circuits are more vulnerable to overload than most people would suspect. And certain elements of society, especially businesses and law enforcement, are a lot more vulnerable to electronic disruption than they would care for us to know about. Perhaps our attention is once again being cynically diverted by experts who have an agenda of their own. But if you pay enough attention, you will occasionally notice a HERF gun in the media.