It probably exists:
...a piece of code that, without people knowing it, uses CPU & GPU power from many people at once
to mine BTC. Thus creating a pool of possibly millions of computers, all generating blocks without even
knowing it.
We've seen incidents such as the high-school IT-guy secretly using the school's computer network to mine.
If I could code such a thing I probably would have. Just like the NASA-system works, where you can sign up
to let your simple home-computer help searching space. Hell, maybe people would even sign-up voluntarily to help mine BTC
through such a network.
There's probably less incentive for such a thing as the difficulty has risen compared to a couple of years ago. But
I had the idea at a time where having a USB Block Eruptor would have made someone a millionaire.
Does it make sense to assume someone might have done this?
A while back it was calculated that a CPU mining bot net was using about $600,000 worth of (stolen) electricity per month to create about $2000 worth of Bitcoins per month.