WhatsApp account can be hacked if one is impetuous, careless and imprudent.

To avoid your WhatsApp account being hacked, please take the following steps

1. Enable FaceID for your WhatsApp Account
2. Enable Two-Step Verification for your WhatsApp Account
3. Do a periodic check of your WhatsApp Settings to know if someone has unauthorised access to your WhatsApp Account

If someone gets hold of your device even for less than a minute they can have your WhatsApp hacked. Do a periodic check of your WhatsApp Settings to know if someone has unauthorised access to your WhatsApp Account. If found, do log them out

Please see the pic below

This feature is provided for you to have access to the same account across all your devices. At the same time, if you are naive, you are hacked!

WhatsApps' Link a Device feature can be used by anyone if you...

1. Have not enabled Guided Access before handing over an iPhone to kids or to a stranger.
2. Have shared your Apple IDs
3. Have shared sensitive information pertaining to your device
4. Have left your iPhone unlocked and unattended in public places like offices, schools, malls etc.

About linked devices | WhatsApp Help Center