WhatsApp may stop working on millions of smartphones early next year. The instant messaging app recently updated its platform support page for multiple operating systems where it said that it is ending support for several old operating systems, both Android as well as iOS. According to WhatsApp, the move is essential to ensure security of its users. Though there’s no exact number available of phones running on these old OSes, media reports suggests that they could be in millions. Here are all the details that you need to know.