Reader Sim Teck How wanted to know what details of his WhatsApp account will be shared with Facebook with the chat app's change in privacy policy. Tech Editor Irene Tham answers.

Last Thursday, WhatsApp made a drastic change to its privacy policy, which allowed it to start sharing user data - including cellphone numbers - with Facebook.

WhatsApp claimed this is to allow Facebook to suggest more phone contacts as friends and display more relevant advertisements. The popular chat app promised "we won't post or share your WhatsApp number with others, including on Facebook, and we still won't sell, share, or give your phone number to advertisers".

But users can still opt out of such sharing. Get moving if you object to the sharing.

If you have received a notice of WhatsApp's new privacy terms, do not simply click on the "agree" button.

Scroll down or click on the "read more" link to turn off the option that reads, "Share my WhatsApp account information with Facebook to improve my Facebook ads and product experiences".

If you have unwittingly accepted the new terms, you can still opt out using the app's settings menu, but only within 30 days of accepting the new terms.

After tapping on the app's settings menu, select "account" and turn off the option that reads "Share my account info".

This will stop WhatsApp from sharing your data with Facebook. But the 30-day opt-out period is a grey area here.

Under Singapore's Personal Data Protection Act, consumers have the right to opt out any time they want.

The Personal Data Protection Commission is seeking clarification from WhatsApp and Facebook on this and other issues.

They include WhatsApp's notification process and what user data it intends to share with Facebook.

Questions have also been raised on whether WhatsApp has done enough to seek consumers' explicit consent for data sharing, as required by the Act.

WhatsApp's privacy change notice is so vaguely worded, there is no way of telling what personal data will be shared and how the data will be used.

For instance, is the sharing limited to a user's phone number, or will his list of contacts be shared too?

It is also not clear if the user's social profile - from the numbers he is in frequent contact with - will be shared with Facebook so that it can suggest more phone contacts as friends.

Consumers should exercise their choice if they value their privacy or are tired of having companies push their boundaries.