Israeli researchers devised a new technique to exfiltrate data from a machine by using a malware that controls hard drive LEDs. Malware can indirectly control the LED, turning it on and off rapidly (up to 5800 blinks per second) Sensitive information can be encoded and leaked over the LED signals, which can then be received remotely by different kinds of cameras and light sensors. The attackers can force the LEDs to blink at a rate of up to 6,000 times per second, which is indiscernible for humans eyes, but potentially readable for light sensors.”]
Source: https://securityaffairs.co/wordpress/56583/breaking-news/data-exfiltration-hdd-leds.html