This is no unofficial hack. According to sources, WhatsApp’s latest update for Android now gives you options on who has access to your “last seen” status – anyone with your number, only your contacts, or no one at all. This new privacy feature also extends to your profile photo and status message (just go to menu -> settings -> account -> privacy).
Other changes in this update include the ability to pay for a friend’s WhatsApp subscription and, you’ll be glad to find that, the mute function for groups finally works.
There’s no given time frame for when this update will be live on the Google Play Store but the apk is already available for download directly from WhatsApp.