Malware Uses Router LEDs to Steal Data From Secure Networks

Specially-designed malware installed on a router or a switch can take control over the device’s LEDs and use them to transmit data in a binary format to a nearby attacker, who can capture it using simple video recording equipment.

https://www.bleepingcomputer.com/news/security/malware-uses-router-leds-to-steal-data-from-secure-networks/