It involves the verification of two steps. Yes, it is not very different from Facebook or Twitter; for example. This type of verification is not exactly new in the application; but most people do not seem to know what it is about. And it can help a lot.
The two-step verification of WhatsApp
To verify your account, you must enter a six-digit code. This is the password you need to enter every time you want to activate the account on another mobile phone. You can also use your e-mail address if you have forgotten your password; although the latter is optional.
Moreover, the application will request this password with some regularity, even if you do not make any changes to your account. This with the aim not to forget it.
Something important: if you activate the verification method in two steps, you have forgotten your password and do not add any e-mail to retrieve it; You must wait at least 7 days to use it on another mobile phone. In this case it should be re-registered, although the app will save your data.
WhatsApp also warns that if you receive an e-mail asking you to disable this authentication and you did not request it, ignore it. This may mean that someone is trying to enter your account from another mobile phone.