It's available to all users. But since it's experimental, you have to go here to enable it: http://www.dropbox.com/try_twofactor http://www.dropbox.com/try_two

It's available to all users. But since it's experimental, you have to go here to enable it: http://www.dropbox.com/try_twofactor http://www.dropbox.com/try_twofactor Then it will appear under Security.