Decompiling can be useful for debugging, analyzing, modifying, or learning from existing code[^2^].

With a debugger you can step through the program assembly interactively.With a disassembler, you can view the program assembly in more detail.With a decompiler, you can turn a program back into partial source code, assuming you know what it was written in (which you can find out with free tools such as PEiD - if the program is packed, you'll have to unpack it first OR Detect-it-Easy if you can't find PEiD anywhere. DIE has a strong developer community on github currently).

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As you have indicated decompilation has been around for a long time and these techniques are available for most mature platforms including .NET (this is true of disassembly also). Obfuscators are a popular option for folks seeking an additional layer of protection. I would add that explicit statements from the copyright owner about usage and decompilation is incredibly important. We have made it clear that using the decompiler does require the permission of the copyright holder and further that it is an optional feature.

It is rare for code to be compiled as written. Most compilers these days will drastically change your code to optimize it. So when you decompile, the compiler can only guess at what the source code must have looked like, it has no way of knowing what your code was, because that's gone. If the decompiler is good, the code you get will at least be compilable back into an equivalent executable, and then you can start slowly refactoring it to be readable. But most likely the decompiler will produce absolutely unreadable spaghetti code, and it will be a huge headache to decipher it. Sometimes, it might end up being less work to just re-write the program from scratch.

News 28/Oct/2012: The Boomerang source code has been converted from CVS to Subversion back in 2008;I've finally changed the instructions so that users will get the Subversion repository now.If you are working with a CVS copy, please generate diffs now while the CVS repository still exists.To help with this, the CVS instructions are still available here.I intend to delete the CVS repository in about a month, say early December. 3/Nov/2006: Gerard Krol has volunteered to become the new project admin. He hopes he will be able to help people interested in Boomerang using and understanding it, and he will try (with your help) to make Boomerang the finest decompiler available.We still suffer the loss of our main developers, so please contribute! 18/Sep/2006: The two main developers of Boomerang, QuantumG and Mike Van Emmerik, are withdrawingfrom further development of Boomerang. This is because both have joined a company that owns technologysufficiently similar to that of Boomerang that there is a conflict. Both will be able to answer emailqueries about how Boomerang works at present, but will not be able to comment on suggestions for changes.For more details, see this news item. 15/Sep/2006: The making page has a link to qt-4.1.4-vs2005.zip, which savesa lot of time and effort if compiling the Boomerang GUI with Visual Studio 2005. 14/Sep/2006: The Visual Studio 2005 project file is finally sorted out, so both the console and GUI(Qtgui2) versions of Boomerang can be made with Visual Studio 2005. 5/Sep/2006: The Windows-only GUI version of Boomerang is now deprecated. It has some problems with thehandling of clusters in threads, which there is no time to fix. If you want to continue using the Windows-onlyGUI, you can start with boomerang-win32.vcproj and work from there. The boomerang.vcproj file now makes theconsole version of Boomerang, which is a prerequisite for the qtgi2 version. Also deprecated are the XML loadingand saving facilities, and the transformation parser. Removing the xml code has the effect of making the Cygwinversion runnable again (no idea why).13/Jun/2006: A new alpha release (0.3) is now available for download. See the download page. For source code, use the CVS tag alpha-0_3.7/Jun/2006: QuantumG has started a blog chronicaling his daily activity on a new Qt4 based GUI for Boomerang, along with general Boomerang development and (eventually) other projects he is working on.12/May/2006: Sourceforge have changed the names of the CVS servers. That means that existingrepositories will not work as they stand. You can change the name with a few Unix commands like this:Create a file called changeit with this contents:mv $1 $1.oldsed -e s/@cvs\.sourceforge\.net/@boomerang.cvs.sourceforge.net/ $1.old > $1chmod +x changeitfind . -name Root -exec /absolute/path/to/changeit \;Try to execute this command only once, otherwise the Root.old files will be overwritten.Of course, if you have made no changes to your checked out source, you can just get a freshcheckout. The changes are listed in the FAQ question13, but the only changeis from cvs.sourceforge.net to boomerang.cvs.sourceforge.net.(Also note that the ":80" as was used on the cvs page doesn't workany more either.)We are sorryfor the inconvenience, but this is out of our hands. 10/Apr/2006: Cygwin doesn't seem to be able to compile the loader/MachOBinaryFile.cppsource code, so until some kind soul who knows about such things can fix it, using theMachOBinaryFile loader is now disabled if the host is Cygwin.At least that way, a Cygwin hosted Boomerang will compile, and can decompile programs other thanin the MachO binaryfile format.

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