In Mac OS X 10.5.8 whenever I download an app etc, then open it I get the "This app was downloaded from the internet are you sure you want to open it" dialogue. Never did it with Tiger... Does anyone know how to turn it off?
The quarantine feature is new as of Mac OS X 10.5 - it's designed to make it more obvious what is new software when you first run it. (Primarily to help protect users from trojan horse attacks). Apple has made all the really deep technical details of it's file quarantine feature available.
To disable it you need to run:
in the Terminal. You'll need to restart for it to take effect.
On existing files you can run