There are many .Net code protection alternative, that obfuscate
the IL codes so that they are not that much exposed to IL disassembler application.
- .Net Reactor
- Themida
- SmartAssembly
- the list is huge . . .
many of the protector modify the Exe (PE Header info), .Net exe contains some extra MetaData that helps disassembler to identify it.
Download this little application it may tell you a little more about the exe.
Download PEiD 0.95
PEiD is an intuitive application that relies on its user-friendly
interface to detect packers, cryptors and compilers found in PE
executable files – its detection rate is higher than that of other
similar tools since the app packs more than 600 different signatures
in PE files.
PEiD comes with three different scanning methods, each suitable for a
distinct purpose. The Normal one scans the user-specified PE file at
its Entry Point for all its included signatures. The so-called Deep
Mode comes with increased detection ratio since it scans the file's
Entry Point containing section, whereas the Hardcore mode scans the
entire file for all the documented signatures.
My best guess the assembly you are looking for is Protected by .Net Reactor
or Themida