Change the WhatsApp email privacy settings to prevent unknown numbers from adding you to newsgroups without your permission.

WhatsApp is one of the most widely used mobile messaging systems in the world. In addition to the ability to send messages at no extra cost, no matter where your loved ones are located, WhatsApp is extremely convenient for managing group discussions.

But sometimes you can find yourself invited to chat groups with complete strangers without really knowing why. However, it is possible to restrict invitations to group conversations to only the contacts in your address book. 

1. Open the Application Settings

Launch WhatsApp and go to Application Settings. Then enter the Account menu and access the Privacy options.

2. Allow groups for your contacts only

Then enter the Groups menu, and change the default setting, Everyone (which allows any WhatsApp user with your number to add you to a group conversation), to My Contacts, or My Contacts Except....

If you choose this second option, you will be prompted to select the contacts in your address book that you want to prevent from adding you to group conversations without your consent.

Source: 01net.com