Guilds are what i am looking for!
Since the chances to get any reward by some computers is almost zero, i rather use their work to get some "fixed" rates from those so called guilds.

I would use run the mining only outside of office times, there is no harm at all.
Also i do not need permission to use "computers of my employees", since its my little office and i bought those computers.

Can you suggest any guild?
Computers will run 16hrs a day for mining, 3650 MH/s in total.

I want - at least - the income of our coffee consumption