there are numerous applications around on the net that you can download and allow to run while your computer isn’t doing anything else to lend your computing power to a bigger project. seti@home is the most well known example. now a way has been found to exploit the checksum procedures that form part of the tcp protocol to harness the power of computers on the net:

parasitic computing represents an ethically challenging alternative for cluster computing, as it uses resources without the consent of the computer’s owner.