It appears that Adobe closed some major security concerns with Flash Player 10.0.42.34 see here, however I believe these security concerns have changed the ability to access swf when setting Security.allowDomain.

ASDOC says:

“If two SWF files are served from different domains — for example, http://siteA.com/swfA.swf and http://siteB.com/siteB.swf — then, by default, Flash Player does not allow swfA.swf to script swfB.swf, nor swfB.swf to script swfA.swf. A SWF file gives SWF files from other domains by calling Security.allowDomain(). This is called cross-domain scripting. By calling Security.allowDomain(”siteA.com”), siteB.swf gives siteA.swf permission to script it.” > see here.

In the example below I am creating the example ASDOC is describing. I will create two application which will be hosted on two separate domain names, however I am unable to change properties in the accessed application, see detail below:

Accessed application will holds a label and set the Security.allowDomain to wild card (*) so any application should be able to load this swf and change properties. See below:

<Application xmlns:fx="http://ns.adobe.com/mxml/2009"
			   xmlns:s="library://ns.adobe.com/flex/spark"
			   xmlns:mx="library://ns.adobe.com/flex/halo"
			   minWidth="1024" minHeight="768" preinitialize="application1_initializeHandler(event)">
	<fx:Script>
		<![CDATA[
			import mx.events.FlexEvent;

			protected function application1_initializeHandler(event:FlexEvent):void
			{
				Security.allowDomain("*");
			}

		]]>
	</fx:Script>

	<Label id="label" text="Hello from accessed application!"  x="8" y="9"/>

</s:Application>

The second application (accessing application) will be hosted on a separate domain and load the accessed swf and change the label property:

<Application xmlns:fx="http://ns.adobe.com/mxml/2009"
			   xmlns:s="library://ns.adobe.com/flex/spark"
			   xmlns:mx="library://ns.adobe.com/flex/halo"
			   minWidth="1024" minHeight="768"
			   initialize="initializeHandler()">
	<fx:Script>
		<![CDATA[
			import mx.controls.Alert;
			import mx.events.FlexEvent;

			// define variables
			private var loader:Loader;
			private var content:*;

			// load swf
			private function initializeHandler():void
			{
				loader = new Loader();
				loader.contentLoaderInfo.addEventListener(SecurityErrorEvent.SECURITY_ERROR, securityErrorHandler);
				loader.contentLoaderInfo.addEventListener(Event.COMPLETE, loadContent_onComplete);
				loader.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler);
				loader.load(new URLRequest("http://zeen.com/temp/bin-debug/AccessedApplication.swf"));

				component.addChild(loader);
			}

			// Event Handler

			private function loadContent_onComplete(event:Event):void
			{
				content = event.target.content;

				var onContentApplicationComplete:Function = function(event:Event):void
				{
					// content loaded successfully
				}

				content.addEventListener(FlexEvent.APPLICATION_COMPLETE, onContentApplicationComplete);
			}

			private function ioErrorHandler(event:IOErrorEvent):void
			{
				loader.contentLoaderInfo.removeEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler);
				Alert.show(event.text);
			}

			private function securityErrorHandler(event:SecurityErrorEvent):void
			{
				loader.contentLoaderInfo.removeEventListener(SecurityErrorEvent.SECURITY_ERROR, securityErrorHandler);
				Alert.show(event.text);
			}          

			// methods to access loaded swf

			private function callAccessedApplication():void
			{
				this.content.document.label.text = "label change!";
			}

		]]>
	</fx:Script>

	<mx:UIComponent id="component" width="400" height="82" x="11" y="43" />

	<Button label="Call accessed application"
			  click="callAccessedApplication()" x="84" y="0"/>   

</s:Application>

I also have set the cross-domain policy on the accessed applciation server to allow access:

<!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
   <allow-access-from domain="*"/>
</cross-domain-policy> 

The swf is loaded successfully, but with a warning alert. Additionally, I am unable to change the label properties on the accessed application, see screen shot below:

The application is hosted here:
http://eladelrom.com/bin-debug/AccessingApplication.html

I am hoping to get a clarification: https://bugs.adobe.com/jira/browse/FP-3513