If you want to protect your work, DComSoft SWF Protector is a great encryption solution for your SWF files.
It’s available for Windows, Mac and Linux and it’s free to try. You get a fully functional copy when you download it.
The interface is really intuitive.

You won’t be wasting your time trying to learn how the software works.
With a couple of clicks you’ve protected your SWF file.

You can protect more than one file at a time and all those files are still protected amazingly fast for you.

The size increase in the SWF files I tested was about 20KB which in most situations these days can be disregarded and it is well worth. This will depend on the amount of ActionScript involved. Some only increased 8 or 9 KB.
There is also an “Advanced mode” in which you can choose to ignore some of the Classes.
In this case I may want to deselect all the Greensock Classes as these are not mine.

This also allows you to save some KB, if required.
DComSoft SWF Protector works with both ActionScript 2 and 3 files.
All the functionality and protection you need available here.