A two-stage attack could allow spies to sneak secrets out of the most sensitive buildings, even when the targeted computer system is not connected to any network, researchers from Ben-Gurion University of the Negev in Israel stated in an academic paper describing the refinement of an existing attack.
The technique, called AirHopper, assumes that an attacker has already compromised the targeted system and desires to occasionally sneak out sensitive or classified data. Known as exfiltration, such occasional communication is difficult to maintain, because government technologists frequently separate the most sensitive systems from the public Internet for security. Known as an air gap, such a defensive measure makes it much more difficult for attackers to compromise systems or communicate with infected systems.
Researchers bridge air gap by turning monitors into FM radios
I doubt the average PC user will ever have to worry about this,