The new policy which just went into effect in Europe allows Facebook to harvest information from any partner websites you’ve browsed (outside Facebook), and use it to deliver ‘tailored’ adverts within your feed.
It also allows the social network to collect information from any partner apps you’ve used (pretty much any mainstream iPhone and Android app).
If you opt to tell Facebook where you are - for instance, by using the Nearby Friends feature - the site will also deliver adverts about nearby places such as restaurants and shops.
For anyone concerned about their privacy, the new terms mean, for instance, you could see adverts based on a site you’ve browsed at a later time - perhaps when others are looking at your machine.
The adverts which ‘follow’ you won’t just appear in Facebook, they’ll appear on any website with which Facebook shares your profile information.
Sadly, the way Facebook’s terms and conditions work mean that opting out is difficult - ad-blocking software will help, and Facebook offers an opt-out page (although this is dependent on other advertisers honouring the agreement).
If you are logged in to Facebook on your phone, or in your internet browser, the network will automatically track sites you visit, what you do there, and what you do within apps on your phone.
Although there are ways to limit the way this information is used, there is no way to remove it entirely without deleting or deactivating your Facebook account.
Facebook does offer an Ad Preferences tool, which users can use to complain about targeted adverts – but only after they’ve seen them.
Measures such as using a browser’s ‘Do Not Track’ button have no effect – Facebook ignores this.
If you are browsing sites you would prefer not to remain on an invisible ‘web history’ which is shared with sites around the web, the safest option is not to be logged into Facebook, either on a mobile device or within your browser.