Researchers at the Ben-Gurion University in Beersheba, Israel demonstrated how this can be carried out. They sent a small quadcopter drone one evening early in 2017 from the parking lot of the University and flew it towards a nearby building. They then trained the drones built-in camera on a desktop. computer’s tiny blinking LED inside an office on the third floor of that building and managed to silently draw out from the system an optical stream of all the secrets stored within the system to the camera in the drone.”]
Source: https://hackercombat.com/stealing-data-from-infected-computers-blinking-led/