Facebook makes billions of dollars a year because you give it your data, and it uses that data to help advertisers sell things to you.
Cookies – small pieces of data which are stored in web browsers – mean that these advertisements can follow you around the web.
Whether you are on Facebook or YouTube, cookies allow advertisers to know who you are and know that they want to target you because the data on you suggests you're interested in their products.
As Facebook says: "If you've previously received a cookie from Facebook because you either have an account or have visited facebook.com, your browser sends us information about this cookie when you visit a site with the "Like" button or another social plugin.
"We use this cookie information to help show you a personalised experience on that site as well as Facebook," the company says, and states: "We delete or anonymise it within 90 days, and we do not sell it to advertisers or share it without your permission."
The ongoing scandal regarding Cambridge Analytica is based around allegations that this data was not deleted.
- Where does this data come from?
On Facebook this data comes from every imaginable interaction you have with the social media site – including both your personal interactions with Facebook, but also those of other people you're connected to, as well as any third-party apps such as Tinder that works with the company.
Messages you send to your friends, posts you share on your personal page, even the metadata of the files you upload – for instance the location data saved in images – all provide data for Facebook to use.
The company also collects information that other people provide about you, such as identifying you in the photographs they share of you – although the "tag suggestions" feature (which automatically suggested a Facebook friend to tag) was declared illegal in the EU after the Irish Data Protection Commissioner (DPC) audited Facebook in 2011 and 2012.
- How is this data actually used?
While some of this information is used to allow friends and family to find you and add you on Facebook, this is mainly limited to profile information.
The real information – where Facebook makes its billions – is in the material that users like and share and that is collected and brokered across a range of apps, games, and services which tie-in to the social media platform.
Neil Brown, the director of law firm decoded:Legal told Sky News: "Most people will know the saying 'there's no such thing as a free lunch', but they may not know how companies providing free-of-charge online services make their money.
"In many cases, this involves being shown content paid for by third parties, and what you get shown is often based on what the company knows, or suspects, about you, based on what you post and how you use the web.
"Having clear information about how a site uses your data is a fundamental part of the right to privacy as, without it, users cannot make informed choices about whether to use a site or not."
- Is the information clear?
Facebook users can control how advertisers and third-party apps see their data by going into their settings and defining the material listed under 'Apps' and 'Ads'.
This is also where the site says it provides 'clear information' about how it uses your data.
Facebook founded and CEO Mark Zuckerberg has said that in response to the growing Cambridge Analytica scandal, these buttons will be moved to the top of Facebook users' News Feed to be more easily accessed.
In what may prove to be the most significant move from the social media company in terms of its bottom-line, Mr Zuckerberg said the company will "restrict developers' data access even further to prevent other kinds of abuse.
"For example, we will remove developers' access to your data if you haven't used their app in three months," he wrote – bringing that policy in-line with its activities towards web-browsing cookies.
Facebook will also "reduce the data you give an app when you sign in – to only your name, profile photo and email address".
"We'll require developers to not only get approval but also sign a contract in order to ask anyone for access to their posts or other private data," Mr Zuckerberg said.
- 'This isn't a scandal, this is Facebook's business model'
"Privacy on Facebook is a contradiction in terms," said Silkie Carlo, the director of Big Brother Watch.
"This 'scandal' isn't a data breach, but rather Facebook's business model laid bare. People have finally been confronted with the democratic risks of big data exploitation that privacy advocates like us have been warning about for years."
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"We also need to ask what kind of influencing could Facebook do in pursuit of its own commercial or political interests, or even in response to government pressures, with its 2.2 billion profiles," Ms Carlo told Sky News.
"The risks of our personal information being exploited and our opinions being manipulated are inherent to Facebook as a platform and people need to make an informed choice about whether they're willing to be put at that risk."
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Sky News
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