Code Obfuscation

Whatever you will do they'll be able to see your code, check your algorithm and workaround it. So sad, you're deploying instructions manual! Obfuscate with an Obfuscator if you want but what I strongly suggest is to move your license check in a less obvious place.

• Put all your license related code in a separate DLL.
• Sign it.
• Pack it inside your executable resources (with a not so obvious name) and do not deploy DLL.
• Handle event AppDomain.AssemblyResolve, when your DLL will be needed at run-time you'll unpack in memory and return its stream of bytes. See more about this technique in this Jeffrey Richter's post.

I like this method because they'll see there is a license check but...they won't find license code. Of course any good cracker will solve this issue in 10 minutes but you'll be (little bit more) safe from random ones.