I use Gmail and in that we can find a 2-step verification system for to login. By this option activated, we will get an Verification code SMS from Google and asks to enter that code. Similarly, Twitter also introduced verification system to login.To get started, Login into your account, go to Settings->Account and find an option which says 'Require a verification code when I sign in'. To enable it, you must add a phone number. There are several carriers to choose, so choose your operator.
After entering your number you will able to receive a verification code to your mobile device. It will not ask code, if your browser cache is enabled. Watch below video to start.
Enable it immediately for better security.
Note: This is not enabled in some countries. So, it may not work for some of them.
[Source: Twitter Blog]
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