Most trainers are flagged as "False Positives" because of how they interact with game files. Temporarily disable your shields or add an exception.
While many exist, two of the most trusted names in the community are: Known for stable trainers with clean interfaces.
Version 1.04 was the final official patch for Zero Hour, fixing major bugs and balancing multiplayer. However, it also solidified the difficulty of the AI. Using a trainer allows you to:
Your units and buildings take zero damage from enemy fire.
Unlock your entire secondary ability tree immediately.
Usually, you should start the trainer first, then the game. Listen for a "Trainer Activated" voice cue or look for an active status in the trainer window.