Is it possible for sites like these to harness the computing power of its users in order to mine bitcoins? I thought I read it somewhere but it didn't make sense to me at all since I wasn't aware how a website could access it's users GPUs (or at least it seemed like it would have to be very inefficient and CPU driven). Was this a myth or is this a real thing?
Used to be a real thing, but now I'm not sure. It is pretty easy to test. If your laptop fan comes on when you go to said website site, they might be using your GPU/CPU to do some mining so the fan comes on to cool it off. Thing is, each individual computer is pretty inefficient at mining now unless it is custom built for the task.