I wanted to test the protection of ex4 files with the last versions (MT4 600+ builds). So I have tried different techniques.
I have tried python decompiler, debuggers, x86 disassemblers, hexadecimal edition to remove time and usage limitations.
What is interesting is that each time you will compile your mq4 file, the ex4 will be totally different.
Example with a first compilation :
A second one, seconds later :
The first part define the nature of the file. There is probably a characters count at the beginning as you can't remove parts of the code without breaking it. The encryption probably depends on the file modification date.
At this moment and since 2014, there is still no proof that a MT4 600+ builds mq4 file has ever been decompiled. All the service that propose to decompile them are scams.
However, as MT4 is able to translate them on charts, we can suppose that one day a technique will be able to decypher the procedure.