Many Americans this week got their first looks at fake Facebook ads placed by Russian propagandists during the 2016 election campaign to sow discord in the US. The ads, made public during congressional hearings with social-media executives, targeted Americans on both sides of divisive issues such as Islam, gun rights, and the Black Lives Matter movement.

One ad, nominally from an account called Heart of Texas, showed silhouettes of cowboys behind a map of America with a rainbow flag and a poster about Islam taking over the world. "Get Ready to Secede!" the ad screams at the bottom. Another ad shows the somber image of policemen in uniform carrying a casket at a funeral with the words, "Another Gruesome Attack on Police By a BLM Movement Activist."

Psychologists and students of advertising say the ads were cleverly designed to look like other internet memes, and to appeal to readers' emotions. Jay Van Bavel, an associate professor of psychology at NYU, says he was surprised at the sophistication of the campaign. "It wasn't transparent lies. It was just pushing our buttons," says Van Bavel. "To me, this is more pernicious. It's not a matter of fiction that we can root out with fact-checking. It's more about turning Americans against each other."

The ads took issues that voters care about and then "fed them to us as aggressively as possible," he says.

Facebook estimates that 10 million people saw the paid ads and up to 150 million people saw other content from the fake accounts, which Facebook has traced to the Internet Research Agency, a Kremlin-backed troll farm. The ads were placed by fake accounts with names like United Muslims of America, Blacktivist, and LGBT United that could have passed for real Facebook groups.

"The IRA are not amateurs, they're clearly familiarizing themselves with the kind of content that resonates with the target audiences," says Renee DiResta, researcher with Data for Democracy, a nonprofit group that has been digging into the data on Russian-linked accounts.