Frankly, you can't prevent decompilation by a determined professional hacker.
Obfuscators will slow them down (and prevent decompilation by non-experts) but you need to have some serious intellectual property to protect for it to be worth paying several hundred dollars for the better ones.
Visual Studio includes a free version of Dotfuscator and there are also a number of other free ones listed in this thread:
VulpesPosted Jun 28, 2012, 11:37 AM
Obfuscators will slow them down (and prevent decompilation by non-experts) but you need to have some serious intellectual property to protect for it to be worth paying several hundred dollars for the better ones.
Visual Studio includes a free version of Dotfuscator and there are also a number of other free ones listed in this thread:
http://stackoverflow.com/questions/2161201/free-net-obfuscator