As part of a series on extremism on the internet, Marketplace's Molly Wood explores how people get radicalized online.
From This Collection
Extremists online: How a troll becomes a terrorist
Extremists are far too at home on social media. Whose job is it to root them out?
What if social media treated extremist content like junk mail?
A former Facebook policy worker says platforms have a lot to lose if they don't crack down on misinformation.
How internet 'echo chambers' lead to faster radicalization
"Large media corporations have a duty to take on this challenge," one expert says.
More extremists are getting radicalized online. Whose responsibility is that?
And what can social media companies do to intervene?