Ethernet cards also used to run the LED off a transistor that keyed off of the data on the TX and RX lines which would reveal some of the bits as well.
I don’t recall how they fixed that, but it was a big deal at the time. Capacitor? Optical diode?
I believe I recall people using white-out or paint on the LEDs they couldn’t afford to replace.
Edit: if you think about it, wire protocols have error correction built in. Most of them don’t negotiate the amount to use, it’s baked into the spec. When you’re eavesdropping you lose signal to noise ratio. When the input signal is very clean, there’s plenty of SnR to spare. It’s easier to listen to a loud argument than a quiet conspiracy.
I don’t recall how they fixed that, but it was a big deal at the time. Capacitor? Optical diode?
I believe I recall people using white-out or paint on the LEDs they couldn’t afford to replace.
Edit: if you think about it, wire protocols have error correction built in. Most of them don’t negotiate the amount to use, it’s baked into the spec. When you’re eavesdropping you lose signal to noise ratio. When the input signal is very clean, there’s plenty of SnR to spare. It’s easier to listen to a loud argument than a quiet conspiracy.