This is a false positive. It will trigger from time to time with trainers no matter where on the internet you get them from. It is purely because of the way that trainers work. There is nothing harmful in them.
Even if a trainer worked fine before, antiviruses can randomly decide not to like it someday for no apparent reason.
Adding WeMod as an exception resolves this issue.
Here’s more information: Windows Defender marked WeMod as a Trojan.