Hello. 
This is called a false positive. It will happen with trainers every now and again, no matter where on the internet you get them from. It is triggered because of how trainers work (injecting code into memory addresses that a game is running on in your PC’s RAM). They’re harmless.
Please consider using the search button before posting, as this has already been addressed many times. This thread here, for example, will explain in better detail why it happens and how to resolve it: My antivirus marked WeMod as a Trojan - #2 by Ravenfyre.