Otherwise known as two-factor authentication, this optional feature adds an extra layer of security to users’ accounts. To enable it, users need the latest version of WhatsApp and should then navigate to Settings > Account > Two-step verification > and Enable. Once this feature is turned on, users will have to enter a six-digit passcode every time they register their phone number with WhatsApp again. So, for example, if you get a new phone but keep the same SIM card and number.
WhatsApp’s implementation isn’t like two-factor authentication with Google or Facebook, which generates a code with an app or sends one via text. You’ll have to remember your WhatsApp passcode, or you can set-up a backup email, which will allow you to disable two-factor on your account if you ever forget your six-digit passcode. You can also disable two-factor from within the app, without a passcode.
And although you won’t need to use the passcode every time you open the app, WhatsApp will ask you for it “periodically” (The Guardian says every seven days) “to help you remember” what it is.