It feels like every day you read about a new security breach on a website, in many cases involving weak passwords. It's a known fact that users are notoriously lax when it comes to choosing their passwords, so there needs to be a better way of providing secure logins to your site. That's where two-factor security comes in. It aims to complement your existing login scheme by also providing an alternative verification method (generally a cellphone) to validate that a user is, who they say they are. It's a scheme in use by top sites such as Twitter and GMail and has proven to be very reliable in minimizing intrusions via weak passwords.
In this screencast, I'll introduce you to a great service called Authy which provides a platform to build two-factor authentication right into your site.