On a ThinkPad X1 Carbon Gen 8, it's easily possible record video with the webcam LED off. I did not verify newer generations of the X1 Carbon.
Lenovo put a little physical switch—they call it "ThinkShutter"—that serves to physically obstruct the webcam lens to prevent recording. It's supposed to have only two positions: lens obstructed or not. But if the user accidentally slides it halfway, you can still record video with the lens unobstructed but somehow the webcam LED turns off. It's because the ThinkShutter actually moves 2 pieces of plastic: 1 to cover the lens, 1 to cover the LED. But the piece covering the LED blocks it first, before the other piece of plastic blocks the lens. I discovered this accidentally yesterday while toying with a X1 Carbon... I am reporting it to Lenovo.
They fail to develop a reliable webcam indicator, and patch that with some half-assed attempt at physical view obstruction. The whole approach is a demonstration of bad engineering and unreliability. And that's just the part that became public.
I think that its easier to compare the shutter to airplane windows.
The windows are there just to make the humans inside more comfortable, similar to how many people would be more comfortable without a camera pointed at them.
Flashing firmware is a big hill to climb for bad guys in most peoples worlds.
I suppose covering the LED is a less expensive way to provide the same user experience as hooking an electrical switch to the ThinkShutter to electrically turn off the LED when it's in the "blocked" position.
The malware posts comments like OP to lots of hacker oriented message boards, prompting all curiously minded ThinkPad X1 Carbon Gen 8 owners to verify that the comment tells the truth by trying it for themselves.
Lenovo put a little physical switch—they call it "ThinkShutter"—that serves to physically obstruct the webcam lens to prevent recording. It's supposed to have only two positions: lens obstructed or not. But if the user accidentally slides it halfway, you can still record video with the lens unobstructed but somehow the webcam LED turns off. It's because the ThinkShutter actually moves 2 pieces of plastic: 1 to cover the lens, 1 to cover the LED. But the piece covering the LED blocks it first, before the other piece of plastic blocks the lens. I discovered this accidentally yesterday while toying with a X1 Carbon... I am reporting it to Lenovo.