Facebook is going to start hoovering up your WhatsApp data and using it for ads. Unless you tell it not to.

WhatsApp has provoked ire by announcing that it is to start sharing its user data with parent company Facebook, despite assurances at the time that it was bought that everyone’s data would remain entirely private. The company says that the information will be used for ads on Facebook and WhatsApp, as well as helping to improve the messaging platform.

But many people are angry that some of their most personal information – their chats – could potentially be compromised as part of the deal with Facebook.

Now it has emerged that there is a hidden way of opting out of the terms, and ensuring that no data is sent over to Facebook. But it has to be done quickly.

There are two main ways of opting out of the new terms, one of them fairly simply and the other ever so slightly more complicated.

The first way can only be done if you haven’t accepted the new terms, using the pop-up that will emerge when you open up WhatsApp. If you haven’t, wait until that happens but don’t click “agree” – instead navigate to the smaller “read more” option, and untick the box that says “Share my WhatsApp account information with Facebook”.

If you’ve already accepted those new terms, you can still opt out – as long as it’s within 30 days. You can do that by heading to the settings menu in the app, and pressing on the account tab – there you’ll find a “share my account info” button that you can undress and revoke your permission.

It isn’t clear that opting out of the new terms will change the experience at all, either when compared with people who are still having their data shared with Facebook, or with before WhatsApp introduced the change. WhatsApp say that the new change is meant only to help improve the ads on Facebook, so the only possible consequence is that what you see on the network might be slightly less relevant.