WhatsApp always focuses on Security of their users and now WhatsApp make A bold decision to disable the sport for all old version of OS including Nokia, Android and iOS Operating Systems dew to security risk.
From Know platform will not work on these devices as under detail
List of effected Smartphones and OS
Whatsapp will not be available for All Nokia old devices including Symbian OS S60 and S40, BlackBerry 10 also lose Whatsapp support, for android and iOS will followed by OS versions
For iOS: WhatsApp no longer available on iPhone 3G and 3Gs and all devices these having iOS 6 or lower versions
For Android: All Android devices these having android version 2.2 and below
For Android: All Windows devices these having windows 7 and below
WhatsApp did not specify the deadline until January 30, 2017. After that date they will not be able to use WhatsApp either.
WhatsApp is the most popular platform in the world with millions of users, is said to have made such a decision because there are innumerable open risks in older operating system versions. If they use the older phone, they will have to switch to a new smartphone.