understand from some articles that there are decompiler tools that can decompile Aspnet DLL into sourceCode like C#,Vb.net and other supported languages by .netframework.
So, is that means Aspnet DLL of your application can be decompiled into sourceCode and there is no protection.
It might help if you use NGen to generate native DLL first, but then again you need to know exactly what version of .NET the target platform is running, and which type of CPU it's using.
However, since .NET have to support reflection, it still leaves significant amount of information in the DLL and can decompile easier than other type of DLLs.
So, it means that it is not saved to host your aspnet application in Web Hosting service??
Note that it's still relatively more "secure" than ASP, PHP, JSP, etc. as their pages are saved in plain script text. And even Java binaries can be decompiled.
If you're really that concern about "security", you might take a look at CGI programming. They're normal console application (that could have been written in whatever language) so it's relatively difficult to decompile (really, you can't stop someone decompile
it to ASM codes), however their functionalities are quite limited.
Then you can also write your ISAPI extension in C++ to directly intercept the call and emit the pages. An ISAPI can do lots of things, but it's very difficult to written and get it correct. And web hosting companies seldom (if not possible at all) allow you
to install such a thing on it, because that'd essentially give permission for you to access web pages of others running in the same application pool.