The 30 day "opt out" period for many Whatsapp users whose information will be shared with Facebook is coming to a close.

Whatsapp announced new terms and conditions last month which, controversially, will see phone numbers given to its social network parent company. Users were given 30 days to opt out of the arrangement.

With the announcement made in late August, that window of opportunity is about to close for many subscribers.

The sharing of user information, including phone numbers, is part of plans to allow businesses send messages to people, or as Whatsapp puts it, to “improve Facebook ads and product experiences”.

Over a billion people use the app for free messaging. They can opt out of having their data used for ad targeting on Facebook but will not be able to stop the data being shared with the network.

Facebook has more than 1.7 billion active monthly users.

Whatsapp users had two ways of opting out. Firstly, before accepting the new terms service and privacy policy sent out, they could tap the “read option”.

This would lead to a control at the bottom of the screen. “If you do not want your account information shared with Facebook to improve your Facebook ads and products experiences, you can uncheck the box or toggle the control,” it said.

Secondly, where users had selected the agree option, they automatically entered the additional 30 day opt-out period.

This is achieved by going to “settings”, “account” and “share my account info” settings and, again, unchecking the box or toggle the control.