In late 2016, WhatsApp decided to quietly improve the security of its iCloud backups, where messages and contacts are uploaded to Apple servers. According to Forbes, it added a unique encryption key created by the WhatsApp app, rather than just relying on the iCloud Drive to protect customer data.
This means that someone who had somehow acquired access to iCloud data would have an especially hard time getting at any of the WhatsApp data held within, the article adds. On top of the end-to-end encryption rolled out across one billion WhatsApp users, it's become “significantly more difficult for anyone to intercept comms on the app,” Forbes adds.
WhatsApp offers secure messaging and calling. Its voice and video calls use your phone's Internet connection, instead of your cell plan's voice minutes, so you don't have to worry about calling charges.