Source: WhatsApp
If you want to link your WhatsApp account to the PC or the web, the messaging service now requires you to use biometric info to do so. The Facebook-owned company added this protection layer to limit someone else's chance of linking your account without your knowledge.
As long as your smartphone has a face or fingerprint unlock activated, WhatsApp will require you to go through the authentication process. Afterwards, you'll need to scan a QR code using your phone. This security feature is enabled by default, but it won't be triggered if face or fingerprint unlock is switched off completely.
WhatsApp emphasizes that it won't have access to your biometric information. This feature works in tandem with your mobile device getting notifications when someone logs into your account on the web or a computer.
Source: Engadget