Research 10+ years ago found that activity lights on many network cards and switches at 10BaseT could reveal actual network traffic. Very quickly, major device

Research 10+ years ago found that activity lights on many network cards and switches at 10BaseT could reveal actual network traffic. Very quickly, major device manufacturers switched to buffered activity LEDs and the attack became useless. I remember at one point modems switched from flickering with actual traffic to just slow blinking with activity.