Popular cloud storage solution, Dropbox has begun enabling two-step verification for their accounts, which means in addition to your password (something you know), they send an additional access code to your phone, or let you generate a time-based code with a mobile app like Google Authenticator (something you own). Although no security scheme is unbreakable, two-factor authentication is absolutely better than one. And if you keep personal data in Dropbox, you're absolutely going to want to use it.