Dropbox is en route to bring a new, optional, two-step login verification to its desktop service.
The verification will be invoked if you or someone else tries to access your Dropbox account from an unrecognized account.
The verification itself will be done with a password of some sort which will either be sent to you by sms or through a verification app (perhaps Android, iOS, etc.)
You could install the new, experimental, build of Dropbox to enable the two step verification feature – you can do so here. You can also wait a “few days” to get the option through a stable build.
Source | Via