WhatsApp have warned users to update their app to the latest version to make them safe from attack by hackers.
Last week, Facebook, the company that owns WhatsApp discovered a vulnerability to users of the app and rolled out a security patch for it on Friday.
Facebook first discovered the security exploit earlier on in the month and has just pushed out a fix for the issue.
The exploit uses the voice calling feature within the app to install surveillance software on the mobile device. The software would be installed even if the user doesn't pick up the call.
Facebook have published an advisory warning to security experts about the bug.