I am the maintainer of a site that has allegedly 'lost' the source code to a flash swf file. How do I decompile this source?
This is a possible solution: http://www.darknet.org.uk/2007/09/flare-flash-decompiler-to-extract-actionscript/
Usually 'lost' is a euphemism for "We stopped paying the developer and now he wont give us the source code."
That being said, I own a copy of Burak's ActionScript Viewer, and it works pretty well. A simple google search will find you many other SWF decompilers.
erlswf is an opensource project written in erlang for decompiling .swf files.
Here's the site: http://code.google.com/p/erlswf/
Get the Sothink SWF decompiler. Not free, but worth it. Recently used it to decompile an SWF that I had lost the fla for, and I could completely round-trip swf-fla and back!
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I've had good luck with the SWF::File library on CPAN, and particularly the dumpswf.plx tool that comes with that distribution. It generates Perl code that, when run, regenerates your SWF.