Installing App Inventor Set up

[chiara...@gmail.com]

I've downloaded the App Inventor Setup.pkg but I can't open it. An error message comes up which says can't be opened "because it comes from an unidentified developer" (see attached image)

HELP! 

[stefan...@gmail.com]

Go to system preferences, then security, then click the box that says something like "allow third party apps to install"