WhatsApp stopped working on millions of Android and iOS devices running older operating systems, as the company moved to protect its users, Forbes reported.

Since 1 February, the app was reported to be no longer accessible on phones running Android version 2.3.7 and older, along with iPhones operating iOS 8 or earlier.

The media outlet stated millions of smartphones were affected by the update, which was announced in 2017.

“Because we no longer actively develop for these operating systems, some features might stop functioning at any time. For the best experience, we recommend you use the latest version of iOS or Android available for your phone”, WhatsApp wrote in a blog.

In 2016, Facebook’s subsidiary announced its withdrawal from several mobile platforms, including BlackBerry 10, followed by a move to end support for smartphones using Windows from the end of 2019, BBC News reported.

The messaging service was the third most-downloaded app in the past decade, data from analyst company App Annie showed.