An electromagnetic attack uses radio-frequency or other EM signals to influence hardware or to capture information it unintentionally emits. Unlike passive side-channel monitoring, an active attack may inject energy into a device and then measure the resulting response, making hidden behavior easier to observe. The target can be a cable, peripheral, chip, or entire system, depending on the coupling path.
This matters in cyber security because hardware is not silent: clocks, displays, audio circuits, power lines, and antennas can leak data through electromagnetic emissions. Attackers use that leakage to recover keystrokes, audio, or cryptographic activity, while defenders test for susceptibility with shielding, filtering, grounding, and emission scanning. Good physical-layer security reduces the chance that a normal device becomes an unintended transmitter or a probe point for signal extraction.