A new version of easyXDM 2.4.17 is out. It's marked as a critical update and contains a fix to the easyxdm.swf that addresses a "possible XSS attack vector".
FlashTransport is uses for messaging only after SameOrginTransport and PostMessageTransport can't be used. According to the easyXDM website FlashTransport is used for IE6 and IE7.
For the update replace the easyxdm.swf and easyXDM.js files with the newer ones.