Most Flash & Flex files can be decompiled, revealing the source code to anyone who makes the effort to do so. Unfortunately, it doesn’t require a great deal of effort to download one of the many decompilers available online and rip off someone else’s hard work.
I did a lot of research looking for a solution, and most of the SWF protection packages out there don’t actually deliver what they promise. They are simply too easy to outsmart. However, after scouring many technical forums and developer sites, I found that a large number of developers are using irrFuscator.
Ambiera’s irrFuscator obfuscates the Actionscript 3 bytecode in Flash and Flex SWF files so that decompilers won’t be able to extract your function, variable and constant names anymore. irrFuscator can read in a directory of .as and .mxml files, process them and put them out into a target directory. Simply recompile the directory with the obfuscated files and your .swf files are a lot safer.
In contrast to many other SWF ‘protectors’, irrfuscator doesn’t ‘encrypt’ the SWF, it obfuscates the code, removing all the information from it. In this way, it cannot be ‘decrypted’ because the information simply isn’t there anymore. That’s why many big browser game and website developers, like Blizzard & Bigpoint, rely on the protection irrFuscator provides. You can see the list on their site.
You can try a free download at Actionscript Obfuscator.