A former employee of Cambridge Analytica who claims the firm used the personal data of tens of millions of Facebook profiles to allegedly help Donald Trump's election campaign, is to testify before US Congress. Christopher Wylie said he had accepted an invitation to give evidence to the US House Intelligence Committee and House Judiciary Committee this week. He disclosed last month that the political consultancy firm had harvested data from users of the social media site by using personality quizzes to build up psychological profiles. As the US election approached, he said it then used this data to target them with bespoke political advertising. His revelations triggered investigations in the UK and US.

The Facebook crisis involving Cambridge Analytica's data breach leads many to question how Facebook treats their users' data; Reaction on'Outnumbered.' The man who revealed the Cambridge Analytica data-harvesting scandal said Sunday he believed the political consulting firm snatched information from more than the previously reported 87 million Facebook users. "I think that there is, you know, a genuine -- a genuine risk that this data has been accessed by quite a few people. And that it could be stored in various parts of the world, including Russia, given the fact that, you know, the professor who was managing the data harvesting process was going back and forward between the U.K. and to Russia," Christopher Wylie said on NBC News' "Meet the Press." Wylie was referring to Aleksandr Kogan, whose company, Global Science Research, harvested Facebook's data using a personality app, according to officials.