As per the info given by Whatsapp team, WhatsApp won’t work in millions of mobiles from February 1st as the WhatsApp is getting updated and it won’t be supporting in the outdated devices like iPhones having software older than IOS 7 will no longer be supported and also won’t support any Android device with version 2.3.7 installed. Hence to avoid this issue in your mobile just keep your mobile updated with latest software.