How to Write a Multi OS Backdoor in Java
I have written a Java backdoor available at http://pastebin.com/2nYicFPM, If you have any questions, please comment and I will update the tutorial on the part you find difficult to understand. This is due the code being long and it just makes it easier to explain the harder parts of it only without me having to explain everything.
If you want native code instead of JVM bytecode, you could use gnj compiler, however the exe will only work on the platform you compiled it in. You could also use excelsior jet.