"Ten years ago, I was working in military intelligence and I could feel the power, and could see how technology is implemented," Manning, once jailed for leaking classified information, said at the C2 Montreal business conference.
Manning said she is stunned now by the "dramatic change in policing style, and aggressive (government) surveillance."
It is "getting worse, especially in the United States," she added.
She urged programmers and computer scientists working on artificial intelligence and machine learning "to consider the ethical implications of the technology that they are building and developing."
Manning, now 30, was an army intelligence analyst sentenced to 35 years in prison in 2013 for leaking more than 700,000 classified documents related to the wars in Iraq and Afghanistan.
The revelations by Manning, who is transgender and was then known as Bradley Manning, exposed covered-up misdeeds and possible crimes by US troops and allies.
Her actions made Manning a hero to anti-war and anti-secrecy activists, but US establishment figures branded her a traitor.
Then-president Barack Obama commuted her sentence, leading to her release in May 2017.
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