Two factor authentication requires a user to have two discreet pieces of secret data to access an account. For example a password and a secret code sent to your phone. Hacking a two-factor authentication requires the scoundrel to have both your password and your phone. It is increasingly important as we all embrace the cloud. Dropbox just announced its own support for two factor authentication and I'm already in. To get started, click the security setting for your account at the Dropbox web site. Strangely, I didn't see an iOS application for two factor authentication. Instead, Dropbox sends me a text message with a six digit number.
Dropbox's particular flavor of two-step verification kicks in whenever you log into the web site or attempt to add a new device. This really isn't that intrusive and much more secure. If you use Dropbox, go do it now.