A new WhatsApp update will see millions of users unable to use the messaging service from today.
Several iPhone and Android phones which have outdated operating systems will not be supported on the app.
Smartphones using Android 2.3.7 and iPhones with iOS 8 or older will be affected by the update.
However, users who update their phone's operating system should be able to use the app.
In a statement, a spokesperson for WhatsApp said: "This was a tough decision for us to make, but the right one in order to give people better ways to keep in touch with friends, family, and loved ones using WhatsApp."
Irish Independent Technology Editor, Adrian Weckler, explained the decision was made due to security reasons.
He said: "From today, WhatsApp will no longer work on a whole array of old smartphones, both iPhones and Android phones.
"WhatsApp is saying it is cutting off these phones because it needs to make sure that the security of WhatsApp is up to date and it can't guarantee that on these old phones.
"When I say old phones, what I mean is old operating systems."
It comes after a similar move at the end of 2019 that saw Windows phones lose support for the instant messager.