Is it possible to prevent decompilation of .NET MSIL DLL?

Question

Almost all the .net assemblies can be de-compiled using Reflection .Which means that all .net products are open source since the code can be easily be used by other developers. Isnt there a way so that we can encrypt the codes (at least for some security logic) so that it cannot be easily cracked or misused.

Edit

Old question Is winforms .net really equal to open source? was edited considering comments regarding proper use of the word Open Source

Answer 1

There are tools that can encrypt .NET Assemblies, preventing decompilation with Reflector and similar tools. They also perform a number of related services such as obfuscation, protection of embedded resources, etc. Two I know of:

RemoteSoft Salamander Suite
XHEO DeployLX