I wrote this app years ago, for my own personal use, never published it anywhere.
I wondered if a virus might have been able to infect it, but even restoring the exe from six years ago doesn't solve the problem.
I haven't managed to find anything useful on how this trojan is detected, which might enable me to change whatever it is in my code that provokes this.
(I'm also not sure whether this is the right place to ask the question)