If you want to play the game safely and support the developers who are still active today, here is the best way to get it: The Best Way to Play: Battle Realms Zen Edition

While the game is over 20 years old, it is not "abandonware." Because the Zen Edition is actively sold and maintained:

The original creator, Ed Del Castillo, and his team at Liquid Entertainment are still actively patching the game to improve balance and graphics. Why Avoid "Free" Abandonware Sites?

Join the official to find community guides and players for the Kenji’s Journey campaign or skirmish modes.

Check for frequent sales—it is often available for a very low price.