Today, Twitter has rolled out a new security feature that helps prevent account hacking. List most other high-profile sites, they’ve started offering two-factor authentication. This means in addition to your regular password, you can setup your account so that you need to enter a six-digit code that is sent to you via text message.
1) Go to Twitter and click on the Settings gear in the top toolbar of the site.
2) Go to Settings.
3) Scroll down to Account Security (which should be just below Password Reset) and check the box and follow the prompts.
4) The next time you login, you’ll be prompted by a screen asking for the verification code they sent to your phone.
If you don’t see the option, check back later. It shouldn’t take long, but they’re probably doing a gradual rollout.
Source: Twitter Blog