There are many ways to protect your swf file from being stolen, right from encrypting it with obfuscatory or making them domain dependent with this.url property. However these is also a more dedicated and determined way to prevent swf theft in general. This has benefits as well as cons.
You can try to discourage swf theft by preventing swfs from appearing in browser cache. This can be done with the Apache .htaccess file. Simple add following lines to your site’s .htaccess file, that lies at the root of your site.
Header unset Cache-Control:
Header append Cache-Control: "no-cache, must-revalidate"
Header set Cache-Control "max-age=0, private, no-store, no-cache, must-revalidate"