irrFuscator is an ActionScript 3 obfuscator. It can protect .SWF files as well as .AS and .MXML files. irrFuscator is available for the command line but also comes with a convenient GUI frontend. It is able to encrypt strings, strip whitespace, does nondeterministic obfuscation and automaticly detects references to external flex code.

The ActionScript 3 Byte Code (abc) in .swf files still contains a lot of symbols revealing how your program works and what it does, so it is very easy to reverse engineer or steal your code. irrFuscator can be used in two modes:
SWF Obfusction (Binary): protects an existing .swf file.
Flex Obfuscation (Source): reads in a directory of .as and .mxml files, processes them and puts them out into a target directory. Simply recompile the directory with the obfuscated files and your .swf files are a lot safer.

Features :

Obfuscation: It changes the names of functions, methods, constants, interfaces and classes using a deterministic or not deterministic naming scheme if wished. Unlike other basic source level obfuscators, irrFuscator will also rename your classes (and the files they are located in accordingly) in source mode.
String encryption: Strings in your code are automatically encrypted if wished.
Built-In flex call recognition: irrFuscator will not obfuscate calls to any of the flex libraries so your code will compile of course.
Optional automatic stripping of code comments and/or whitespace: If you want to give away your source code, this option is very useful.
Speed: irrFuscator is written in C++ and needs only about 10 seconds to obfuscate one megabyte of source code on a standard developer PC. For a binary .swf file, it usually needs less than one second.
Tested: irrFuscator is used by huge flex based projects like the Darkness Springs Role Playing game which contains more than 100.000 lines of code.
Obfuscation exceptions: If you need a symbol to be visible outside of your code or you are using dynamic classes, you can specify any symbol not to be obfusctated. In this way, irrFuscator can also be used with the flash development environment where you have a .fla file and several .as files. (irrfuscator will only obfuscate the .as files)

Platform: Windows 98, Windows Me, Windows 2000, Windows XP, Windows 2003, Windows Vista

System Requirements: 256 MB RAM, any processor