Investigations by The Guardian and The New York Times published a year ago prompted the ICO to seize Cambridge Analytica's computers and servers as part of their own inquiry in March 2017
A UK consultancy working on Donald Trump's US election campaign pleaded guilty and was fined by a London court Wednesday over its refusal to release personal data it secretly hovered off Facebook.
The social media giant has admitted that Cambridge Analytica - a political advisory that ran Trump's digital outreach in 2016 - used an app to collect the private details of 87 million users without their knowledge.
It then strategically targeted them with political ads and produced detailed polls that allegedly helped Trump score an upset victory over Democratic hopeful Hillary Clinton.
Cambridge Analytica pleaded guilty on Wednesday of failing to comply with a UK media regulator's order to release the information it had on a US professor who demanded to know what the company knew about him - and how.
It was fined £15,000 and required to pay around £6,000 in court costs.
Wednesday's hearing in a tiny courtroom in the residential outskirts of London was a test case that provided a glimpse into a scandal that has rocked Facebook's reputation and provided more work for US investigators probing Trump's campaign.
An attorney representing the UK Information Commissioner's Office (ICO) media regulator told the court that Cambridge Analytica managed to gather what amounted to 81 billion printed pages of data about Facebook users.
Investigations by The Guardian and The New York Times published a year ago prompted the ICO to seize Cambridge Analytica's computers and servers as part of their own inquiry in March 2017.
The firm has since gone into administration.
But Wednesday's hearing showed that Cambridge Analytica is still putting up a fight.
An ICO attorney said the London-based company had initially told US Professor David Carroll that his request for information was groundless because he was neither a British citizen or resident.
"You have no right to make a data access request - any more than a member of the Taliban sitting in a cave in the remotest corner of Afghanistan," Cambridge Analytica's letter to him said.
One of the company's executives later told the ICO that he did "not expect to be further harassed with this sort of correspondence."
The company's guilty plea was also carefully crafted.
Cambridge Analytica admitted to a "failure to comply with (an ICO) enforcement notice."
But the plea notes that "this prosecution does not relate to nor suggest misuse of data or any potential action relating thereto."
'Not done yet'
Professor Carroll told AFP that he felt only partially vindicated by the verdict.
"It's another step in the way. We are not done yet," he said in a telephone interview from New York.
"The quest is complete when I get all my data."
Presiding judge Kenneth Grant agreed to look into the specifics of Carroll's data request - but not the wider issue of Cambridge Analytica releasing all the information it had.
Carroll said the biggest revelation from Wednesday's hearing was that the ICO had obtained the passwords to Cambridge Analytica's servers that the company had initially tried not to disclose.
He said this could lead to the eventual release of the data as well as a more thorough review of digital privacy rules in both Britain and the United States.
"I think the story is not over," the US professor said.
The court heard that Cambridge Analytica's guilty plea was coordinated with ICO representatives over the course of the past weeks.
It marked a last-minute change of strategy by administrators who inherited the case from the company's executives.
Cambridge Analytica pleaded not guilty in an initial hearing on October 3.
The ICO called the admission and Wednesday's sentence "a warning that there are consequences for ignoring the law."
"Wherever you live in the world, if your data is being processed by a UK company, UK data protection laws apply," the UK regulator said in a statement released to AFP.