One thing to try is booting an independent OS, such as a Windows diagnostic disc or a Linux Live CD. If there is a hardware problem, you should see the same symptoms. Also check if you can disable the camera in your BIOS: laptop cameras are usually interfaced though an internal USB hub.

Run the Microsoft anti-rootkit tool or Malwarebytes' Anti-Rootkit if you haven't already, just to rule that out.

@AFH: Unfortunately like I mentioned in the post, the symptoms have been gone ever since I taped the paper on (while Wi-Fi was disconnected), so it doesn't even reproduce on the original OS. Camera can't be disabled in the BIOS either on this laptop unfortunately.

@SiXandSeven8ths: Hmm okay~

OK. I didn't realise that the symptoms had gone away permanently.

@SiXandSeven8ths: By the way, for Microsoft's, were you referring to RootKitRevealer, or something else? It seems like it doesn't run on recent Windows versions?

I'm voting to close this question as off-topic because OP describes that the problem is no longer reproducible.

@fixer1234: How the hell does a problem no longer reproducing itself make a question "off-topic"?

There's no way to find if an answer worked, if you can't reproduce the question reliably. Which makes it impossible to proceed past "I saw a light in my PC the other day". I'm inclined to think the closevotes are not bogus in this case.

@JourneymanGeek: I don't follow? Sure there can be ways. Someone might know of a log event I could look for, which might explain what happened if I can spot it. Someone else might know of a recent stealthy virus or something that went around doing something like this, and I could try to find a trace of that if I know what to look for. Lots of potential ways to diagnose the problem even if it's not reproducible; how do you magically know none of them will work?

How do we know it will happen again? Or if its a real problem and not just some hardware glitch? Or even just some transient stray voltage lighting up the LED...

@JourneymanGeek: Wait, what? It's not like if it was reproducible you would magically know what the problem was either, right?? You'd still need to tell me to look for logs or broken wires or something. If I found them that would obviously pinpoint the problem. If I didn't then that obviously wouldn't. So in this case you can tell me to look for the same things you would in that case. I could still look for them and let you know if I found them...

@JourneymanGeek: Bump~

I donno man. I'm still agreeing with the 5 people who voted to close here, and am not inclined to overrule them.

@JourneymanGeek: I mean, why though? I thought I gave a pretty convincing rebuttal why it doesn't really make much difference. Is what I was saying not making sense? Heck, how is this different from a question like this one? Like in this example, I'm sure questions about past events come up all the time here; what's so wrong with this one?

naw, that's a clear set of logs that shows what happened, and asks for it to be interpreted. Its quite different from a transient light going on. Shrug I guess you can take it to meta, but I personally don't think its something I feel strongly enough to modhammer open.

of course it's not a virus. it's a Trojan. someone took control of your computer to spy on you. now they figured out that you will notice the webcam light, so they will try to use less noticeable methods

@SargeBorsch: Are you trolling?

@Mehrdad of course not

@SargeBorsch: Sigh, I don't have time for trolling. But like I said, the webcam turned off while the network was disconnected. Not connected.