How can I limit the size of a file upload?

Question

I am uploading a file using a file reference using the code below.  I want to  limit the file size (bytes) of the uploaded file to 100k, so that a huge file won't crash the browser or my SWF.
What's the best place in the following process to test this, and actually prevent the large file from being loaded?  Is that even possible?
private function uploadImageBtn_clickHandler() : void {
     var arr:Array = [];
     arr.push(new FileFilter("Images", "*.gif;*.jpeg;*.jpg;*.png"));
     fileRef.browse(arr);
private function fileReference_select(evt:Event):void {
     fileRef.load();
private function fileReference_complete(event:Event):void {
     var loader:Loader = new Loader();
     loader.contentLoaderInfo.addEventListener(Event.COMPLETE, loader_complete);
     loader.loadBytes(fileRef.data);
public function loader_complete (event:Event) : void {
     trace("Loader info = "+event.currentTarget.bytesLoaded); // file size in bytes
     var sourceBMP:Bitmap = event.currentTarget.loader.content as Bitmap;
     bgImage.source = sourceBMP; 

Answer 1

Thank you. I just needed to be pointed in the right direction. After looking over this stuff, including FilePermission, I think this may give me what I was looking for. It will be a while before I get to implementing it or testing something like this, I'm just trying to get a grasp on all of the things I need to do and how to approach it.
By doing this I can control how much filespace it can use.
I can control CPU usage by monitoring for extra threads that don't belong and killing or settings the priority on it.
Now I just need to think of something to monitor how much memory the plugin uses. I suppose I could gc, then store the current memory usage, then execute the plugin, gc again, and measure the size again. Does that sound like a reasonable way to estimate it's memory usage? I'm not looking for tiny changes, I just want to see large, substantial increases.