Cambridge Analytica: Why all the controversy?

Cambridge Analytica, a data analytics firm which worked on US president Donald Trump's election campaign and has been linked to Brexit, was embroiled in a storm over Facebook data and dirty tactics.

The company has since said it is shutting down, citing a loss of business after the scandal.

Here are answers to some of the key questions about the British firm.

What was Cambridge Analytica?

Cambridge Analytica was a British company which used personal information from social media users to help clients try to influence voters or consumers, crafting messages targeted specifically to people's hopes, fears or desires.

The firm was founded as an offshoot of SCL Group, a strategic communication and military operations firm, in 2013.

It was largely owned by Robert Mercer, an American billionaire with a history of funding conservative political campaigns, who named Mr Trump's former campaign architect Steve Bannon as vice-president before he stepped into politics.

What did it do?

The firm described itself as delivering "data-driven behavioural change" for its clients in both political and commercial fields, using large amounts of personal data from social media and other sources.

On a practical basis, the company's services were perhaps best described by chief data officer Alex Taylor.

"If you're collecting data on people and you're profiling them, that gives you more insight that you can use to know how to segment the population, to give them messaging about issues that they care about, and language and imagery that they're likely to engage with," said Mr Taylor, in a secretly filmed meeting with Channel 4 News broadcast earlier this year.

"We used that in America and we used that in Africa. That's what we do as a company."

Where did it work?

Cambridge Analytica famously switched from working with Ted Cruz in the 2016 US election to aiding Mr Trump's team, but it had previously helped 44 congressional and Senate campaigns in the 2014 mid-term elections.

Both chief executive Alexander Nix and the leaders of the Leave.EU campaign boasted about working together on the Brexit campaign but have since retracted their claims, saying no contract was signed and no work was completed.

Employees talked of working on political and commercial campaigns around the world in the Channel 4 expose, from Mexico and Malaysia to Brazil, Kenya, Australia and China.

Were its methods effective?

The jury is still out on whether Cambridge Analytica's tactics had the effect it claimed they did, mainly because it is so difficult to measure.

The company boasted about helping its clients by targeting small groups of individuals - middle-aged men who live in Kent and are concerned about immigration, for example - with "psychographic" political advertising which plays to their fears and influences their vote.

However, by definition, the targeted individuals would be the only people able to see the adverts on social media, and they may not even be aware of it.

Managing director Mark Turnbull said: "It has to happen without anyone thinking 'that's propaganda' because the moment you think 'that's propaganda', the next question is 'who's put that out?' So we have to be very subtle."

So what was the controversy?

Top of the list were topics raised by Mr Nix in a meeting with Channel 4 News journalists, in which he discussed "deep digging" on opposition candidates, and disinformation and entrapment as possible tactics for fighting elections, on top of its targeted messaging service.

Facebook banned Cambridge Analytica from using its platform on in March, days before a whistleblower claimed the company had harvested and stored data about more than 50 million Facebook users without their permission.

The majority of those users were in the US but the UK's Information Commissioner issued a warrant to search the company's London offices after it failed to respond to a previous request about the possible illegal use of data.

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