In SWF files running in a version earlier than Flash Player 7, url must be in the same superdomain as the SWF file that is issuing this call. A superdomain is derived by removing the left-most component of a file's URL. For example, a SWF file at
www.someDomain.com can load data from a source at store.someDomain.com because both files are in the same superdomain of someDomain.com.
In SWF files of any version running in Flash Player 7 or later, url must be in exactly the same domain as the SWF file that is issuing this call. For example, a SWF file at
www.someDomain.com can load data only from sources that are also at
www.someDomain.com. To load data from a different domain, you can place a cross-domain policy file on the server hosting the data source that is being accessed.