WhatsApp is banning some iPhone users who are using modified versions of the popular app. All iPhone users without the official version should download it immediately because the ban is made via phone number. Reversing this type of ban is much harder than accounts that use an email or username.
Until now, this type of ban only happened on Android for unofficial apps in the Google Play Store, which added all kinds of features. The top unofficial app is WhatsApp Plus.
WhatsApp has always justified its position by arguing that using unofficial apps puts user security at risk. The official version guarantees end-to-end encryption, which prevents anybody outside a chat from accessing its content. In addition, WhatsApp is concerned that some of these apps contain malware.