Great job on this game! Would definitely like to see something like this with fleshed out characters; it's hard to relate to stick figures.
I want to point out however, the "white box" is Flash player loading the content; not anti-virus or flash player issues... It's either your preloader isn't on the first frame, or the assets are set to load before the preloader. That's why the preloader only appears for a split second after the rest of the content loads. Some evidence of this is if you throttle your internet connection you'll notice the white box will appear longer as it loads the ~50mb of content, and no matter how slow the connection it'll only show the preloader for a split second.
Unfortunately it is something that has to be fixed on your end, and since it's such a large file (for an SWF anyway) you're going to lose people with slower connections that don't realize how much longer it'll take to load.