If you have not noticed they have updated the security section of your dropbox account. You can now enable two factor authentication for your account. Basically it will send a PIN to your mobile device that you append to your password.
I am a big fan of this form of two factor authentication. It just makes sense, the one thing I hate is seeing people walking around with their face in a phone or what ever you want to call them. But the reality is that penetration of these devices especially in younger generations makes this two factor authentication impossible not to have at the top of your list.