Lokesh

You should:

1) Add some verification inside code. This verification should check some registration code before first start. If client has no verification code, then application will not start.

2) You should use Dotfuscator to protect your code from decompilation. Dotfuscator is built-in Visual Studio. Also there are many different tools from 3rd developers.

3) Instead #1 you can use Armadillo or something like that for protection of your product.

Just a comment: if your product is not something like Photoshop or Windows, then it has no sense to build-in complex protection from the hackers. Hackers are lazy now ;) They do not like small software, it is not interesting. Also client need support - it costs more then software and more important for client.

So better to put more time into development and user testing instead hard protection.

Sergey