The background of the recommendation is the exploitation of a weak point in the implementation of Internet telephony (VoIP). However, Facebook claims that only a few selected users may have become the target of attacks.
To update WhatsApp
If the Whatsapp applications have not automatically updated, it is usually sufficient to open the App Store on the device to initiate the update. To be sure, you can then check the version number in the application. This can be found in the Settings under Help, sometimes under Help and then App Info.
These versions are safe
According to the Whatsapp mother Facebook, secure Whatsapp versions have the numbers 2.19.134 (Android), 2.19.51 (iOS), 2.18.348 (Windows Phone) and 2.18.15 (Tizen) or higher. For the business versions of Whatsapp, the numbers should be 2.19.44 (Android) or 2.19.51 (iOS) or higher.
Some smartphones will not be able to update soon
It shows again how important regular updates for security are. However, some devices will soon no longer be supplied with WhatsApp updates. The complete list can be found here:
On these smartphones WhatsApp is turned off