Pretty confident, if the recieving machine is compromised, it is only connected to the opto coupler, that ensures only one way traffic, on one pin.
Somehow you would have to get a receive pin to transmit, and then get through the opto coupler and then it just hits a pin that's designed to only send data.
Somehow you would have to get a receive pin to transmit, and then get through the opto coupler and then it just hits a pin that's designed to only send data.