Elizabeth Denham, the Information Commissioner, wrote in her accompanying report that Facebook should have done more to explain to its users why they were targeted for specific political advertisements or messaging. "But this can not be at the expense of transparency, fairness and compliance with the law", she said in a statement.
The London-based firm worked for Donald Trump's campaign team in the 2016 United States presidential election and used the data to build a software program to predict and try to influence votes.
The report sets out regulatory action taken against a number of the star players in this year's data scandal, including a criminal prosecution against Cambridge Analytica's parent biz SCL Elections Ltd - which has since folded, in name at least - for failing to properly deal with the ICO's enforcement notice.
Just 53 Australians downloaded the "this is your digital life" Facebook quiz app responsible for the Cambridge Analytica data breach.
"It shows the scale of the problem and that we are doing the right thing with our new data protection rules", she said.
However, Sky News notes that the £500,000 fine will be "pocket change" for a company valued previous year at around $590bn (£445bn). She added: 'Trust and confidence in the integrity of our democratic processes risk being disrupted because the average voter has little idea of what is going on behind the scenes.
The ICO fine is a fraction of the amount the social media giant could have faced had a new EU law that gives residents of the European Union more control over their personal data been in affect when the data was shared.
But the ICO said because of the timing of the incidents involved in its inquiry, the penalties were limited to those available under previous legislation.
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According to CNN, before 2015, in some cases when Facebook users interacted with the apps built by third-party developers on the social media platform, the developer not only got data about that user, but also about the users' friends and what they "liked". "People can not have control over their own data if they don't know or understand how it is being used".
That's why greater and genuine transparency about the use of data analytics is vital'.
ICO, which does not normally publish its findings, said it would give the public another update on its investigation in October.
"This can not by left to a secret internal investigation at Facebook".
Facebook has said it will be reviewing the report and responding to the ICO soon.
Damian Collins, the chairman of the U.K. Parliament's media committee, said Wednesday that the company "should now make the results of their internal investigations known to the ICO, our committee and other relevant investigatory authorities".
"The number of Facebook users affected by this kind of data scraping may be far greater than has now been acknowledged".