WhatsApp users will soon have the option of protecting backups of their messages with end-to-end encryption, as the app has begun slowly rolling out the option to iOS and Android users around the world, Facebook CEO Mark Zuckerberg said Thursday on his Facebook page.

WhatsApp, acquired by Facebook in 2014, says the addition is the final step in completing the end-to-end encryption experience and will give its users a level of security and privacy unequaled by any other messaging service.

Previously, WhatsApp messages were encrypted when they traveled back and forth between users, making them scrambled and useless to anyone else if intercepted. But the same couldn't be said for message backups stored in a cloud service. They could've been accessed, for example, by law enforcement officials with a search warrant.

Zuckerberg and WhatsApp originally announced plans to roll out the feature, which is an option for users rather than a requirement, back in September.

With the change, WhatsApp says backups of messages stored in Google Drive or iCloud can also now be encrypted and be accessible only to the user. No one else will be able to unlock and access the backups, not even WhatsApp, Apple or Google.

To create an end-to-end encrypted backup, WhatsApp users should make sure they're on the latest version of the app, then open Settings > Chats > Chat Backups > End-to-End Encrypted Backup and follow the prompts to create one.