A lot of users have asked why Viber won't allow the privacy of it's user by allowing blocking unwanted contacts on the mobile app. But recently viber have allowed the block feature for iOS. With this new feature, you can block any new contact, you don't want to chat with, and they won't be able to call or send you message via Viber.
To block a user, click on their profile
2. You will find the block contact and you will be fine from stalkers or a friends that you don't like
You can always unblock your friend again if they promise to be nice by clicking on the settings tab and find the Block List
All numbers you have blocked will appear on list and you can click the unblock button
Click UNBLOCK and they will appear on your contacts list again.
Note : When you unblock a user, note that it will take you another 48 hours to block them again. So make sure you are absolutely sure you want to unblock them.
Also make sure you have the latest Viber from itunes. The updated Viber with block is is Viber 4.2.1.