Niantic is getting rid of Pokémon Go cheaters with a pretty effective crusade: Deleting their illegally-obtained Pocket Monsters.
The Japanese Pokémon Go Twitter account announced that it would soon be taking some sort of measure to keep the game "fun and fair," and in this case it seems that means combating anyone who attempts to cheat.
Cheating in Pokémon Go is typically achieved with third-party services that can aid you in capturing specific Pokémon, or help you play without actually leaving the home.
Niantic says that any Pokémon caught by players using these services will just be deleted from the game and replaced with a permanent red diagonal line. The Pokémon themselves will effectively become useless slots in your inventory, which isn't anything hardcore players would want to see in their Pokédex, so it should act as a strong deterrent for anyone looking to get ahead using underhanded methods.
With the integration of Pokémon Go into the upcoming Pokémon Let's Go Pikachu and Eevee titles coming soon, it looks like Niantic is doing everything it can to ensure cheaters don't ruin the experience for everyone. The new Switch games will let you transfer your own Pokémon from Pokémon Go into those games, and a whole gaggle of illegal Pokémon will no doubt screw up the balance for players. Plus, and more importantly, cheaters never prosper.
So if you're going to play the new Switch games on the horizon, just play like everyone else and don't try to get ahead using shady methods. It'll just come back to bite you in the end.