A team of Israeli researchers has devised a new technique to exfiltrate data from a machine by using a malware that controls router LEDs. A malicious code is executed on the LAN switch or router, allowing full control of the status LEDs. Sensitive data can be encoded and modulated over the blinking of the LEDs. The generated signals can then be recorded by various types of remote cameras and optical sensors. To prevent this kind of attack the best option for the user it to put a tape over the LEDs, and to check the firmware running his/her router.”]
Source: https://securityaffairs.co/wordpress/59808/hacking/exfiltrating-data-router-leds.html