Many WhatsApp users are about to find themselves cut off from using the hugely popular chat app.

Users of older iPhones and Android handsets are to find the app has stopped working after it said it would stop support from the end of the 2016.

WhatsApp said that the move had been made to ensure that the app could continue to introduce new features and stay secure, which relies on the app being used on newer operating systems. But it has been criticised by many users, particularly those in developing markets where both the app and older handsets are popular.

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Anyone using Android 2.1 or 2.2, an iPhone 3GS or iOS 6 will find the app has stopped working. The same will happen to anyone on Windows Phone 7.

The company has advised that anyone with one of those older handsets who want to keep chatting with friends simply buy a newer phone.

WhatsApp had initially said that all BlackBerry models and some Nokia handsets would also find themselves unable to get onto the chat app. But it walked that back late last year, apparently in response to complaints.

"We are extending support for BlackBerry OS, BlackBerry 10, Nokia S40 and Nokia Symbian S60 until June 30, 2017," it wrote in an update to its blog.

The changes are thought to be in large part to allow WhatsApp to more deeply integrate encryption and other privacy services. Such technology stops messages from being read, and has led to WhatsApp facing criticism from governments who believe that WhatsApp conversations should be made public.