Because trainers work by injecting code into running processes, antivirus software (especially Windows Defender) flags them as "hacktool" or "riskware." This is a false positive due to their behavior, but caution is still required.
Your lord, knights, and archers become invincible. They cannot die to fire, boiling oil, assassin backstabs, or even the Wolf’s trebuchets. Conversely, some trainers offer "One-Hit Kill" for enemy units. stronghold crusader hd 1.3 trainer