I just had a question, If we wanted to modify or change the source code of an expert advisor without having its mq4 file. how can we do ?
I know there are paid services
but i wanna know how can I do ?
Decompiling tools exist but are often unreliable, and the process demands significant technical expertise in assembly language and binary analysis. If you have the knowledge to modify the code successfully, it’s better to develop a new EA from scratch to maintain full control over the code.
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Hi @ved01010. Please don’t decompile an EA that isn’t belong to you. Have a respect to other works. But you can learn how it work and try to develop your own. 
You can decompile only old EA, especially the MQL Market one. It can be done by reading memory block. For example when you declare
int counter; => will be seen ad 3D 03 ... ... (example)
So you need to replace every 3D 03 into … int something.
Since there is cloud protection, the code is also changed. So there is a case a decompile can’t work on different platform build.
Overall, dont care to decompile it … just learn how to develop yourself. Learn how your favorite EA work and try to develop yourself.
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do you want to go to jail?
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how can changing an EA code can get him in jail?! :-/
Years ago, metaqoutes created encrypt extension EX4 to protect developers property against thieves Decompilation EX4 extension or in other words discovering code lines is a violation against copyrights
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That’s why I don’t sell good EAs anymore. I already had a case where my work and my intellectual property was ignored. That’s why from now on there will only be signals from my live account. Thank the thieves.
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I used to think that forums should remove threads like this, which can come across as condoning or even facilitating illegality, but I was wrong: it’s actually worth leaving them up, as a way of drawing to the attention of people looking not only that it’s illegal, but that they can (and really sometimes will) get into big trouble for it.
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there is tons and tons of thiefs stealing on MQL market, doing crazy manipulations and disappearing after, then creating new accounts for doing the same… MQL don’t care, you really think theres a chance of going to jail for decompressing an ex4?
How do you know?
There’s no possibility of that. You can only go to jail for breaking criminal law, not civil law. It’s the difference between “being prosecuted” and “being sued”. So whoever said “going to jail,” that was an exaggeration, but the principle behind it was correct, valid and understandable. 
You really cannot. MetaQuotes compiles their advisors into a binary file, just like any other executable file or library, packs it up and adds additional mechanisms to prevent it from being reverse-engineered. If you could open it in tools like IDA Pro, you would see cryptic stuff that will take AGES to make sense of, making it not worthwhile.