Disable “application downloaded from the internet” message in Mac OS X
You can remove the “Blah is an application downloaded from the internet. Are you sure you want to open it?” on a per application basis by using the following command:
xattr -d -r com.apple.quarantine /Path/to/application/
If you want to remove the that warning message from all in your ~/Downloads directory, you can type the following command:
xattr -d -r com.apple.quarantine ~/Downloads
Remember this method only effects items you choose to specify. If you want to disable this message from ever appearing again for any applications downloaded, learn how to permanently disable the file warning dialogue.