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Rat/ trojan programming
Learn Visual Basic(Old school but its a simple place to start) or Download/get a Trojan source code and read through it dissect it and test it out. Learn whats doing what google commands that are run learn to adapt them to your own needs.
Make sure you set up a VM machine for testing tho dont want to compromise your own system. I do not have any tutorials for you to read through. Im sure google may have a few links for you to read through.