Now, researchers from Tel Aviv University and Technion have gone a step further than past efforts, and found a way to steal data from air-gapped machines while their equipment is in another room.

"By measuring the target's electromagnetic emanations, the attack extracts the secret decryption key within seconds, from a target located in an adjacent room across a wall," Daniel Genkin, Lev Pachmanov, Itamar Pipman, and Eran Tromer write in a recently published paper. The research will be presented at the upcoming RSA Conference on March 3.

"The attack in its current form uses lab equipment that costs about $3000 and, as 
shown in the photos, is somewhat unwieldy," Tromer told Motherboard in an email. "However, experience shows that once the physical phenomena are understood in the lab, the attack setup can be miniaturized and simplified."