Today's Twitter update has a keen focus on security. Back in May, the company introduced an SMS-based two-factor authentication system for signing into the service. Now login requests can be be verified using just the mobile app. Users can sign into Twitter and enjoy the extra security of two-factor authentication without having to provide a phone number or worry about cell reception. The app also generates backup codes just in case your phone isn't available when you want to sign in later on.
Several weeks ago, Dropbox suffered a small security breach that gave wrong-doers access to a few unlucky users' email addresses. On the good side, it also brought the vulnerability to the Dropbox staff's attention. Since then, they've been working hard to beef up security, and today, they introduced two-step verification.
Much like Google's two-factor authentication, once enabled this requires you to login using two different sets of verification: your password and a unique identifier sent in either a text message or generated locally on the device using the authenticator app (which you have the option to get via QR during the set up process).