Mac OS X's: Disable "Downloaded from the Internet" warning message

Prevent annoying warning during the opening of an application 
downloaded from the internet.

Open Terminal and enter sudo xattr -d -r com.apple.quarantine /PATH/TO/APPLICATION

  sudo xattr -d -r com.apple.quarantine /Applications/Steam.app

So what has just happened?

• sudo - allows a permitted user to execute a command as the superuser...
• xattr - display and manipulate extended attributes  
• -d option ('delete'), causes the given attribute name (and associated value), to be removed.
• -r  option ('recursively') If a file argument is a directory, act as if the entire contents of the directory recursively were also specified (so that every file in the directory tree is acted upon)

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