Legally speaking if the game (or whatever) doesnlt make 100% clear what is going on ("we are going to be using your CPU") then I'd say it's very shaky territory.
Also I am pretty sure that in a lot of countries you would be pretty much required to either have a splash saying "click yes to play this game and work some units" or have a workable opt out (I dont know if that exists??)
Legally speaking if the game (or whatever) doesnlt make 100% clear what is going on ("we are going to be using your CPU") then I'd say it's very shaky territory.
Also I am pretty sure that in a lot of countries you would be pretty much required to either have a splash saying "click yes to play this game and work some units" or have a workable opt out (I dont know if that exists??)