Flash can be a great multimedia tool. It can also be a dangerous thing when in the wrong hands. SWFIntruder helps cut through the veil so you can see if Flash apps might be dangerous.
The tool can analyze a Flash application in a semi-automated fashion to detect various security problems like cross-site scripting and cross-site connectivity through Flash itself.
Use of the tool requires Firefox 2.x, which means that it'll run on both Windows and Linux systems. The tool is new, has bugs, and so it isn't all polished and shiny yet. Nevertheless you can download a copy now and try it out.
Check out more details over at OWASP and download a copy of SWFIntruder from the Google Code site