If it was fully undetectable it would mean that it would have no effect and does not exist on disk or in memory of any sort. Any malware/RAT is detectable in so

If it was fully undetectable it would mean that it would have no effect and does not exist on disk or in memory of any sort. Any malware/RAT is detectable in someway since it has some effect that shouldn't be there. That can be network activity, just the process running, just the code existing on a drive or in memory or anything else.