Gases in cooling system and computer question

The heat started blowing cold for awhile and the temp gauge quickly shot up to hot then quickly fell back down to normal and the heat was ok. The shop said no "external coolant leaks at the time. Performed hydrocarbon test and found over 2,000 ppm combustion gases in cooling system. Combustion pressure and gas being introduced into cooling system. This is creating air bubbles in the system and leading to overheating". Since then it runs fine and have put over 1,000 miles without any more problems. Question:can it get worse or can I use a additive like Bar's head sealer to help at this point? Also, is it possible for the computer to be hacked into to cause a temporary problem like this? I'm serious in asking this question. Thanks for your help.