Can be protected from reverse engeneering an app developed in C#?

Answer 1

The short answer is no. Since .NET compiles to the intermediate language (MSIL), the original code can easily be inferred from the compiled assemblies.

However, there are obfuscation utilities that make understanding/modifying the decompiled code much more difficult. They essentially work by renaming all of your variables and method names to useless letters and abbreviations, and rearranging the code to appear in a format that is harder to read by a human without really concentrating and probably taking notes. Again, it is not impossible, but it makes it much more time-consuming (and thus more costly) to make anything useful out of obfuscated code.

The Dotfuscator Community Edition is built into Visual Studio .NET 2003. Search Google for "c# obfuscator" or ".NET obfuscator" for more utilities.

Answer 2

Use an obfuscator:
http://msdn2.microsoft.com/en-us/vcsharp/aa336818.aspx#obfuscators

Answer 3

unfortunately, no. As far as I know any application can be reverse engineered.