Dropbox added two-step verification on their platform couple of days ago. They have now made this feature official.
The company said in a blog post:
Today we’d like to announce the launch of two-step verification, a feature that will enhance the security of your Dropbox by requiring two levels of authentication: your password, and a security code that will either be texted to your mobile phone or generated by a mobile authenticator app (available for iOS, Android, Blackberry and Windows Phone 7).
Accounts on which this feature is enabled would now require two passwords for authentication.