  Air-gapped computers are systems that are kept isolated from the Internet
since they store or process sensitive information.
  In this paper, we introduce an optical covert channel in which an attacker
can leak (or, exfiltlrate) sensitive information from air-gapped computers
through manipulations on the screen brightness. This covert channel is
invisible and it works even while the user is working on the computer. Malware
on a compromised computer can obtain sensitive data (e.g., files, images,
encryption keys and passwords), and modulate it within the screen brightness,
invisible to users. The small changes in the brightness are invisible to humans
but can be recovered from video streams taken by cameras such as a local
security camera, smartphone camera or a webcam. We present related work and
discuss the technical and scientific background of this covert channel. We
examined the channel's boundaries under various parameters, with different
types of computer and TV screens, and at several distances. We also tested
different types of camera receivers to demonstrate the covert channel. Lastly,
we present relevant countermeasures to this type of attack. Lastly, we present
relevant countermeasures to this type of attack.
