FLA is one of these file format that we’re used to freely open without any fear. Our complete confidence is going to change since a new exploit has been found. This exploit enable an attacker to manipulate an FLA file in a way that, when loaded into the Flash CS3 or 8 IDE, it will execute arbitrary code on our machine.
No need to panic, it’s unlikely that too many of the malicious FLA files are floating around. Just don’t run any untrusted FLA files until Adobe will issue the fix.