Through the power supply to hack the computer, for example, pliers.
That says man is not to hack the computer, and remove information from it. But to do this on the PC first you need to install special software that could manipulate the dispenser and the load on the CPU.
This can be useful for specific, isolated computers that are not connected to Internet or any local network, but with which I want to periodically get some data.
Your pre-installed software can:
1) to modulate the speed of the cooler, and a separate device in the room can remove that sound. Transfer rate is very small, but nevertheless can transmit data.
2) changing the load on the CPU and changing electricity consumption, to modulate the power signal cable, removing its device, which is included in parralelno socket (even at a considerable distance). The faster transmission speed and more reliable.
But through the power supply itself this prog in comp is not set, so this is a "special hack" and not just a hacking home password-protected PC.