What a Vista-like message. Apple warns you every time you open almost any kind of file that was downloaded from the internet, which is MOST files these days. There doesn’t seem to be any way to turn it off. It happens with applications, php files, even HTML and jpg files. As a PHP programmer, I can’t stand seeing this message every time I open files that I coded MYSELF. It severely interrupts my workflow.

The commonly suggested method of using terminal to write to defaults does NOT work for me:
defaults write com.apple.LaunchServices LSQuarantine -bool NO

There is another method of manually removing the quarantine flag of the files that you download each time you download them, but this would take more time than just clicking ok in the stupid dialog.

What did work for me was downloading the latest version of Onyx and unchecking the internet warning checkbox. Thank you, Titanium Software!

Note that this does make your computer more susceptible to viruses and trojans if you visit risky sites or blindly open unknown applications. For users like me, this is preferable to the condescending, interrupting workflow Apple has been increasingly favoring lately.

Cancel or Allow?