Laan's steps..

To encrypt the swf, you have two common ways. One is hiding your code and the other one is

confusing your code. But whatever you done to code, you must know that the code you changed

must be executed well by AVM(actionscript virtual mathine). So, that is the real thing of

encrypt swf file: you do something to the code to let the decompiler miss but

the AVM not.

To do this, firstly, you should know the swf file structure. You can download the adobe swf file
format document.Before you do encrypt swf, make sure you are clear to the swf file structure. Secondly, you should know how to encrypt. Sorry to tell you, I konw just one simple way. I copy the DoABC tag abcfile ByteArray to a new tag and set that tag’s id to 72. The 72 tag does not list in adobe official swf file structure document. The hxasm is just uesed that way. Than, create the swf file according to those changed tags.

I had done that works. You can get the air appliction here.The feeling is great when you dig into it. You will find you can do lot of thing to the swf when you deeply understanding of swf file structure. For example, you can merge two (or more if you need) swf file. And also, you can add content, visual or non visual, into a certain swf. That can do add watermark to  a swf. is that great?

However, the most important thing to you is just do it and do not quit. You will be great!