About contact upload
Contact upload is an optional feature that allows us to identify which of your contacts in your device’s address book are also WhatsApp users so that we can add them to your WhatsApp contacts, and quickly update your WhatsApp contacts in case your contacts who are not yet using WhatsApp sign up later. It’s important to note that WhatsApp does not share your contacts with Facebook. Your version of WhatsApp on your device will display the names for your WhatsApp contacts from your device’s address book so that you can easily connect with them.
When you use the contact upload feature and grant WhatsApp access to your device’s address book, WhatsApp will access and upload the phone numbers in your address book on a regular basis, including those of both the users of WhatsApp and your other contacts. If any of your contacts aren’t yet using WhatsApp, we’ll manage this information for you in a way that ensures those non-user contacts cannot be identified. We don’t store these phone numbers and only process them momentarily to create cryptographic hash values which enable us to more efficiently connect you with these contacts if they join WhatsApp. You can control the contact upload feature from your device-based settings.