Dropbox is a popular cloud storage service used by millions of users. Dropbox has had some issues regarding data security, though, and passwords alone have also proven to be an Achilles heel when it comes to protecting online data.
Phishing attacks and many malware variants are designed to trick users into sharing sensitive information like passwords, or surreptitiously capturing them without the user's knowledge. You should have a cross-device security platform in place to detect and block such attacks, but two-factor authentication provides even stronger security that can be so easily compromised.
The standard logon that most people are familiar with involves a combination of a username and password. That may seem like it's two factors since you need both to successfully logon to the account, but it's really only one factor--the password. The fact is that usernames often follow predictable conventions and are easily, so they offer virtually no additional protection.
There are three things you can use to verify your identity: something you have, something you are, or something you know. The password falls under "something you know". Ideally, your passwords are long and complex enough to prevent them from being easily cracked, and you don't share them with others.
Even then, though, passwords alone are not really enough. Given enough time and resources, an attacker can eventually guess or crack the password. And, since the username is trivial, that's all it takes to gain access to an account in most cases.
The idea of two-factor authentication is to also require "something you are" or "something you have" because neither of those can be guessed. "Something you are" includes things like fingerprints, retina patterns, and other biometric identifiers that are unique to each person. "Something you have" would be a key, or a USB token, or something similar that you have to have physical possession of.
The two-factor authentication system implemented by Dropbox relies on a mobile phone or smartphone--"something you have"--as the second factor. You can configure Dropbox two-factor authentication to send a unique code as a text message to your mobile phone, or you can use a smartphone app that supports the Time-Based One-Time Password (TOTP) protocol to generate a unique code instead. Either way, you must be in physical possession of the mobile phone set up in the Dropbox account in order to logon successfully.
What happens if you lose your smartphone? Dropbox has considered that as well. When you enable two-factor authentication, Dropbox provides a 16-digit emergency backup code. You need to write this down and store it somewhere safe in case you need it.
Security involves a balancing act between simplicity and protection--the simpler it is to log in to an account, the less protection it provides. Two-factor authentication involves additional steps and more hassle, but that is the tradeoff for better security, and ensuring that the data you store online with Dropbox remains protected against unauthorized access.