Regarding botnets GPU mining on the sly --
As someone pointed out, that's very difficult as many people would wonder why their office is suddenly 10 degrees hotter than it was last week, with the same outside temperature and/or household climate control settings.
"Last week, my A/C was set at 78 and my office was comfortable. Now it's too hot in there."
Don't you suppose some people would notice their graphics card spinning up its fan a LOT more than usual (which is usually never, unless you're playing a game).
Even CPU mining could be noticeable, as many CPU fans only spin up when the CPU is getting hot from 100% type work.
When PCs start grinding to a halt, the desktop graphics start lagging, etc. that's when people take their PC to the local PC doctor, or they wipe their machine.
BotnetPopulation = BotnetPopulation - 1
P.S. We had this discussion months ago, back in the glory days when BTC were still $18 or more each. Remember -- botnets have a monetary value for their owners. Now that a Bitcoin brings in a lousy $5, it's even less economically worth it to risk giving up an infected PC.
Honestly though, I mine on two machines I use daily. It would be very difficult for me to notice a difference. The fan on the GPUs are still nice and quiet (they're not overclocked), and there's no noticeable difference in heat. I have a window A/C at home set to a specific temperature, and it stays there, regardless of heat output in the room. The other computer is contained in a room of several hundred square feet, so obviously not going to be able to tell a difference in a room of that size.
There's no lagginess on the desktop, except slight lag when scrolling an Excel document, for instance. But not something that someone who didn't have extensive knowledge of desktops wouldn't already know. Games run perfectly, no lag. If the botnet was set to mine very passively, as I have my computers set, it would only lose 5% or less of the total potential production, while being nearly invisible to the user of the computer.
There are more laptops than there are desktops. There are FAR more corporate style desktops than there are gaming rigs. I would be surprised if 1/10th of the PCs out there would be remotely suitable for mining.
Scratch that, more like 1/100, as it seems even among gamers, only 5% has DX11 capable hardware:
http://store.steampowered.com/hwsurveyOk, let's go with 1/100.
Say you have a botnet of 50,000 computers infected with your GPU-mining trojan. 500 effective mining machines (say, 250MH/s each on average), and 49,500 ineffective miners (say, 2.5MH/s). That's a 250 GH/s botnet.
Now, say you have 20 friends who have botnets themselves. 5 TH/s.
I'm not saying it is true (who knows how many computers might be infected except A/V companies), but only that it is possible, and I would not be surprised if a large portion of the current mining capacities were made up of botnets.