"Facebook's closed design means it has no real control, " Ms. Haugen, who worked on the company's algorithmic products, said a US Senate committee.
"Only Facebook knows how it personalizes your feed for you.
" Facebook is hiding behind walls that prevent researchers and regulators from understanding the real dynamics of their system.
Ms Haugen is due to testify before the committee on the draftUK Parliament Online Security Act October 25.
Elizabeth Denham has done more than most to master big technology. But she is alarmed by the power mismatch between democracies and Silicon Valley - and efforts to politicize the regulator she is leaving.
Over the past five years, the stories on the damage done by social media giants followed a boring and familiar pattern.
First of all, the scandal breaks out. Then the cry rises: Something must be done! (See also: Up With This We Will Not Put!)
Then, mirroring the headlines and noise on (ironically) social media, a meeting is called, for which the ambassadors of the tech giants are summoned.
Finally ... not much is happening.
This model has been seen time and time again.
And the common theme in these stories is how some great damage to societyux often fall between regulators, with Ofcom, Advertising Standards Authority and Autorite de la concurrence et des marches, which naturally stick to their remit.
Elizabeth Denham, the Information Commissioner who is resigning next month, has been somewhat of an antidote to this pattern.
Learn more more about Amol Rajan here .