I'm not going to say that it is or is not a botnet, but 70 GH/s is about 21,000 GTX 1080 Ti GPUs. I know of people on these forums that are running several thousand GPUs, so it's not outside of the realm of possibility that this is a giant mining farm in China or elsewhere.
Several thousands it's not 30-40 thousands!! Currently profit is about 1 buck from one 450 bucks gpu like gtx 1070! 200 buck rx 470 bring ~50% more right now.
Maybe they have found some tricks or what is fucking that?