It\'s a standard practice to decompile and reverse engineer .net assemblies.
I\'d like to release some plugin assemblies that will add to existing applications, but
You can use an obfuscator tool, it will help but reverse engineering will still be very possible.
Your users' computer needs to know what it needs to do, so you have to tell it. The owner of the computer has total control over it, and can therefore know himself what you told the computer to do, and he can tell it to do something else.