-- On the outskirts of St. Petersburg, Russia, inside an unassuming office building, people who claim to have worked there say Internet trolls are hard at work, exploiting America's deepest divisions.
When ABC News' Dan Harris and his team walked into the building, it was clear they were not welcome as a man walked up to them, yelling in Russian and ushering them out.
An undercover video that former trolls say they shot in 2015 appears to show tight security and rows of trolls, typing away.
Lyudmila Savchuk, a journalist, told Harris that she'd gone undercover to work in the troll factory for about $700 a month. She said that as part of her job, she'd invent fictional characters and then post under their names with topics carefully selected by her bosses.
"Their favorite topics were guns, immigrants and homosexuality," Savchuk said. "The kind of topics that could invoke blind and negative emotions."
An independent, liberal Russian TV channel also spoke to a man named Alan Beskaev who said he'd worked in the unit that specifically targeted America.
One minute, he said, "you needed to be a redneck from Kentucky and then later you had to be some kind of white dude from Minnesota. ... And then in 15 minutes, you need to be from New York, writing something in black slang."
Beskaev said some of his colleagues even traveled to the U.S. to do research.
ABC News' Patrick Reevell, Jenna Millman and Knez Walker contributed to this story.