If you download a "Free Serverside Executor.exe" from a YouTube video description, here is what you are actually downloading:

These executors function by "infecting" a game’s server. If you execute a script here, you can delete the map, change the sky, or give every player a specific item. It is the ultimate level of control. Can You Actually Get a Server-Side Executor for Free? The short answer is yes , but with a massive catch.