If you are looking for FREE and 100% protection for your SWF. Swflock.com is the solution for your problem. It offers online converting of SWF using your Web Browser (Chrome, Firefox, Safari or IE). Usual free trial SWF encryption tool put watermark in your SWF for the exchange of their free service, but SWFlock.com do not put any watermark in your SWF and they also add some layers of protection including domain locking, trial period and password protection..
After trying some few SWF and decypting it with (SWF Decompiler 4.0) and amazingly there are no expose actionscript code, images, sound and movieclips found while decrypting the encrypted SWF.
Protect your SWF:
It encrypt your code, images, movie clips in a way that SWF Decompilers cannot decrypt your SWF.
It prevent your SWF from running offline and to other domain.
This option will allow your SWF to run only on a specific period of time.
Your SWF will asked for a password on startup.