A Macromedia customer discovered a vulnerability in the Flash 5 Authoring tool based on the undomented undocumented ActionScript command "fscommand:save". Using this command, Vengy was able to create a "Trojaned" Flash movie that, when viewed using the standalone Flash player, would place a malicious script on the viewer's computer.
The following articles give more information, on this and the related "exec" hole and the SWF/LFM-926 virus, which were both discovered in January.
Another Security Hole Found In Macromedia Flash (Newsbytes.com, February 26)
Vengy's Advisory on the Flash "save" Vulnerability