This is arguably the most legitimate reason. A developer might lose their original MQL4 source files due to hardware failure, accidental deletion, or other disasters. If they still have the compiled EX4 (perhaps distributed to clients), decompilation might be the only way to recover their work.

Version 4.0.5 has been distributed as freeware (at least in some channels), lowering the barrier to entry compared to paid decompilers that can cost hundreds of dollars.

Many traders search for tools like or "Ex4 To Mq4 V4 Decompiler Version 4.0 5 Full Version" . They want to reverse-engineer Expert Advisors (EAs) or indicators. This article explains the reality of these tools, the technical evolution of MetaTrader protection, and the risks of downloading cracked software. The Anatomy of MT4 Files: MQ4 vs. EX4

Convert compiled EX4 files back into readable MQL4 source code (MQ4 format).

Example of decompiled code fragment (before cleanup):

Even in these scenarios, decompilation may violate the original developer's copyright and licensing terms. Legitimate use typically requires either (a) being the original author of the code, or (b) having explicit permission from the copyright holder.

Given all the risks and limitations associated with decompilation, traders and developers should consider legitimate alternatives: